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@settitle GNAT User's Guide for Native Platforms
@defindex ge
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@dircategory GNU Ada Tools 
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@copying
@quotation
GNAT User's Guide for Native Platforms , Aug 20, 2018

AdaCore

Copyright @copyright{} 2008-2018, Free Software Foundation
@end quotation

@end copying

@titlepage
@title GNAT User's Guide for Native Platforms
@insertcopying
@end titlepage
@contents

@c %** start of user preamble

@c %** end of user preamble

@ifnottex
@node Top
@top GNAT User's Guide for Native Platforms
@insertcopying
@end ifnottex

@c %**start of body
@anchor{gnat_ugn doc}@anchor{0}
@emph{GNAT, The GNU Ada Development Environment}


@include gcc-common.texi
GCC version @value{version-GCC}@*
AdaCore

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with the Front-Cover Texts being
"GNAT User's Guide for Native Platforms",
and with no Back-Cover Texts.  A copy of the license is
included in the section entitled @ref{1,,GNU Free Documentation License}.

@menu
* About This Guide:: 
* Getting Started with GNAT:: 
* The GNAT Compilation Model:: 
* Building Executable Programs with GNAT:: 
* GNAT Utility Programs:: 
* GNAT and Program Execution:: 
* Platform-Specific Information:: 
* Example of Binder Output File:: 
* Elaboration Order Handling in GNAT:: 
* Inline Assembler:: 
* GNU Free Documentation License:: 
* Index:: 

@detailmenu
 --- The Detailed Node Listing ---

About This Guide

* What This Guide Contains:: 
* What You Should Know before Reading This Guide:: 
* Related Information:: 
* A Note to Readers of Previous Versions of the Manual:: 
* Conventions:: 

Getting Started with GNAT

* Running GNAT:: 
* Running a Simple Ada Program:: 
* Running a Program with Multiple Units:: 
* Using the gnatmake Utility:: 

The GNAT Compilation Model

* Source Representation:: 
* Foreign Language Representation:: 
* File Naming Topics and Utilities:: 
* Configuration Pragmas:: 
* Generating Object Files:: 
* Source Dependencies:: 
* The Ada Library Information Files:: 
* Binding an Ada Program:: 
* GNAT and Libraries:: 
* Conditional Compilation:: 
* Mixed Language Programming:: 
* GNAT and Other Compilation Models:: 
* Using GNAT Files with External Tools:: 

Foreign Language Representation

* Latin-1:: 
* Other 8-Bit Codes:: 
* Wide_Character Encodings:: 
* Wide_Wide_Character Encodings:: 

File Naming Topics and Utilities

* File Naming Rules:: 
* Using Other File Names:: 
* Alternative File Naming Schemes:: 
* Handling Arbitrary File Naming Conventions with gnatname:: 
* File Name Krunching with gnatkr:: 
* Renaming Files with gnatchop:: 

Handling Arbitrary File Naming Conventions with gnatname

* Arbitrary File Naming Conventions:: 
* Running gnatname:: 
* Switches for gnatname:: 
* Examples of gnatname Usage:: 

File Name Krunching with gnatkr

* About gnatkr:: 
* Using gnatkr:: 
* Krunching Method:: 
* Examples of gnatkr Usage:: 

Renaming Files with gnatchop

* Handling Files with Multiple Units:: 
* Operating gnatchop in Compilation Mode:: 
* Command Line for gnatchop:: 
* Switches for gnatchop:: 
* Examples of gnatchop Usage:: 

Configuration Pragmas

* Handling of Configuration Pragmas:: 
* The Configuration Pragmas Files:: 

GNAT and Libraries

* Introduction to Libraries in GNAT:: 
* General Ada Libraries:: 
* Stand-alone Ada Libraries:: 
* Rebuilding the GNAT Run-Time Library:: 

General Ada Libraries

* Building a library:: 
* Installing a library:: 
* Using a library:: 

Stand-alone Ada Libraries

* Introduction to Stand-alone Libraries:: 
* Building a Stand-alone Library:: 
* Creating a Stand-alone Library to be used in a non-Ada context:: 
* Restrictions in Stand-alone Libraries:: 

Conditional Compilation

* Modeling Conditional Compilation in Ada:: 
* Preprocessing with gnatprep:: 
* Integrated Preprocessing:: 

Modeling Conditional Compilation in Ada

* Use of Boolean Constants:: 
* Debugging - A Special Case:: 
* Conditionalizing Declarations:: 
* Use of Alternative Implementations:: 
* Preprocessing:: 

Preprocessing with gnatprep

* Preprocessing Symbols:: 
* Using gnatprep:: 
* Switches for gnatprep:: 
* Form of Definitions File:: 
* Form of Input Text for gnatprep:: 

Mixed Language Programming

* Interfacing to C:: 
* Calling Conventions:: 
* Building Mixed Ada and C++ Programs:: 
* Generating Ada Bindings for C and C++ headers:: 
* Generating C Headers for Ada Specifications:: 

Building Mixed Ada and C++ Programs

* Interfacing to C++:: 
* Linking a Mixed C++ & Ada Program:: 
* A Simple Example:: 
* Interfacing with C++ constructors:: 
* Interfacing with C++ at the Class Level:: 

Generating Ada Bindings for C and C++ headers

* Running the Binding Generator:: 
* Generating Bindings for C++ Headers:: 
* Switches:: 

Generating C Headers for Ada Specifications

* Running the C Header Generator:: 

GNAT and Other Compilation Models

* Comparison between GNAT and C/C++ Compilation Models:: 
* Comparison between GNAT and Conventional Ada Library Models:: 

Using GNAT Files with External Tools

* Using Other Utility Programs with GNAT:: 
* The External Symbol Naming Scheme of GNAT:: 

Building Executable Programs with GNAT

* Building with gnatmake:: 
* Compiling with gcc:: 
* Compiler Switches:: 
* Linker Switches:: 
* Binding with gnatbind:: 
* Linking with gnatlink:: 
* Using the GNU make Utility:: 

Building with gnatmake

* Running gnatmake:: 
* Switches for gnatmake:: 
* Mode Switches for gnatmake:: 
* Notes on the Command Line:: 
* How gnatmake Works:: 
* Examples of gnatmake Usage:: 

Compiling with gcc

* Compiling Programs:: 
* Search Paths and the Run-Time Library (RTL): Search Paths and the Run-Time Library RTL. 
* Order of Compilation Issues:: 
* Examples:: 

Compiler Switches

* Alphabetical List of All Switches:: 
* Output and Error Message Control:: 
* Warning Message Control:: 
* Debugging and Assertion Control:: 
* Validity Checking:: 
* Style Checking:: 
* Run-Time Checks:: 
* Using gcc for Syntax Checking:: 
* Using gcc for Semantic Checking:: 
* Compiling Different Versions of Ada:: 
* Character Set Control:: 
* File Naming Control:: 
* Subprogram Inlining Control:: 
* Auxiliary Output Control:: 
* Debugging Control:: 
* Exception Handling Control:: 
* Units to Sources Mapping Files:: 
* Code Generation Control:: 

Binding with gnatbind

* Running gnatbind:: 
* Switches for gnatbind:: 
* Command-Line Access:: 
* Search Paths for gnatbind:: 
* Examples of gnatbind Usage:: 

Switches for gnatbind

* Consistency-Checking Modes:: 
* Binder Error Message Control:: 
* Elaboration Control:: 
* Output Control:: 
* Dynamic Allocation Control:: 
* Binding with Non-Ada Main Programs:: 
* Binding Programs with No Main Subprogram:: 

Linking with gnatlink

* Running gnatlink:: 
* Switches for gnatlink:: 

Using the GNU make Utility

* Using gnatmake in a Makefile:: 
* Automatically Creating a List of Directories:: 
* Generating the Command Line Switches:: 
* Overcoming Command Line Length Limits:: 

GNAT Utility Programs

* The File Cleanup Utility gnatclean:: 
* The GNAT Library Browser gnatls:: 
* The Cross-Referencing Tools gnatxref and gnatfind:: 
* The Ada to HTML Converter gnathtml:: 

The File Cleanup Utility gnatclean

* Running gnatclean:: 
* Switches for gnatclean:: 

The GNAT Library Browser gnatls

* Running gnatls:: 
* Switches for gnatls:: 
* Example of gnatls Usage:: 

The Cross-Referencing Tools gnatxref and gnatfind

* gnatxref Switches:: 
* gnatfind Switches:: 
* Configuration Files for gnatxref and gnatfind:: 
* Regular Expressions in gnatfind and gnatxref:: 
* Examples of gnatxref Usage:: 
* Examples of gnatfind Usage:: 

Examples of gnatxref Usage

* General Usage:: 
* Using gnatxref with vi:: 

The Ada to HTML Converter gnathtml

* Invoking gnathtml:: 
* Installing gnathtml:: 

GNAT and Program Execution

* Running and Debugging Ada Programs:: 
* Profiling:: 
* Improving Performance:: 
* Overflow Check Handling in GNAT:: 
* Performing Dimensionality Analysis in GNAT:: 
* Stack Related Facilities:: 
* Memory Management Issues:: 

Running and Debugging Ada Programs

* The GNAT Debugger GDB:: 
* Running GDB:: 
* Introduction to GDB Commands:: 
* Using Ada Expressions:: 
* Calling User-Defined Subprograms:: 
* Using the next Command in a Function:: 
* Stopping When Ada Exceptions Are Raised:: 
* Ada Tasks:: 
* Debugging Generic Units:: 
* Remote Debugging with gdbserver:: 
* GNAT Abnormal Termination or Failure to Terminate:: 
* Naming Conventions for GNAT Source Files:: 
* Getting Internal Debugging Information:: 
* Stack Traceback:: 
* Pretty-Printers for the GNAT runtime:: 

Stack Traceback

* Non-Symbolic Traceback:: 
* Symbolic Traceback:: 

Profiling

* Profiling an Ada Program with gprof:: 

Profiling an Ada Program with gprof

* Compilation for profiling:: 
* Program execution:: 
* Running gprof:: 
* Interpretation of profiling results:: 

Improving Performance

* Performance Considerations:: 
* Text_IO Suggestions:: 
* Reducing Size of Executables with Unused Subprogram/Data Elimination:: 

Performance Considerations

* Controlling Run-Time Checks:: 
* Use of Restrictions:: 
* Optimization Levels:: 
* Debugging Optimized Code:: 
* Inlining of Subprograms:: 
* Floating_Point_Operations:: 
* Vectorization of loops:: 
* Other Optimization Switches:: 
* Optimization and Strict Aliasing:: 
* Aliased Variables and Optimization:: 
* Atomic Variables and Optimization:: 
* Passive Task Optimization:: 

Reducing Size of Executables with Unused Subprogram/Data Elimination

* About unused subprogram/data elimination:: 
* Compilation options:: 
* Example of unused subprogram/data elimination:: 

Overflow Check Handling in GNAT

* Background:: 
* Management of Overflows in GNAT:: 
* Specifying the Desired Mode:: 
* Default Settings:: 
* Implementation Notes:: 

Stack Related Facilities

* Stack Overflow Checking:: 
* Static Stack Usage Analysis:: 
* Dynamic Stack Usage Analysis:: 

Memory Management Issues

* Some Useful Memory Pools:: 
* The GNAT Debug Pool Facility:: 

Platform-Specific Information

* Run-Time Libraries:: 
* Specifying a Run-Time Library:: 
* GNU/Linux Topics:: 
* Microsoft Windows Topics:: 
* Mac OS Topics:: 

Run-Time Libraries

* Summary of Run-Time Configurations:: 

Specifying a Run-Time Library

* Choosing the Scheduling Policy:: 

GNU/Linux Topics

* Required Packages on GNU/Linux:: 

Microsoft Windows Topics

* Using GNAT on Windows:: 
* Using a network installation of GNAT:: 
* CONSOLE and WINDOWS subsystems:: 
* Temporary Files:: 
* Disabling Command Line Argument Expansion:: 
* Mixed-Language Programming on Windows:: 
* Windows Specific Add-Ons:: 

Mixed-Language Programming on Windows

* Windows Calling Conventions:: 
* Introduction to Dynamic Link Libraries (DLLs): Introduction to Dynamic Link Libraries DLLs. 
* Using DLLs with GNAT:: 
* Building DLLs with GNAT Project files:: 
* Building DLLs with GNAT:: 
* Building DLLs with gnatdll:: 
* Ada DLLs and Finalization:: 
* Creating a Spec for Ada DLLs:: 
* GNAT and Windows Resources:: 
* Using GNAT DLLs from Microsoft Visual Studio Applications:: 
* Debugging a DLL:: 
* Setting Stack Size from gnatlink:: 
* Setting Heap Size from gnatlink:: 

Windows Calling Conventions

* C Calling Convention:: 
* Stdcall Calling Convention:: 
* Win32 Calling Convention:: 
* DLL Calling Convention:: 

Using DLLs with GNAT

* Creating an Ada Spec for the DLL Services:: 
* Creating an Import Library:: 

Building DLLs with gnatdll

* Limitations When Using Ada DLLs from Ada:: 
* Exporting Ada Entities:: 
* Ada DLLs and Elaboration:: 

Creating a Spec for Ada DLLs

* Creating the Definition File:: 
* Using gnatdll:: 

GNAT and Windows Resources

* Building Resources:: 
* Compiling Resources:: 
* Using Resources:: 

Debugging a DLL

* Program and DLL Both Built with GCC/GNAT:: 
* Program Built with Foreign Tools and DLL Built with GCC/GNAT:: 

Windows Specific Add-Ons

* Win32Ada:: 
* wPOSIX:: 

Mac OS Topics

* Codesigning the Debugger:: 

Elaboration Order Handling in GNAT

* Elaboration Code:: 
* Elaboration Order:: 
* Checking the Elaboration Order:: 
* Controlling the Elaboration Order in Ada:: 
* Controlling the Elaboration Order in GNAT:: 
* Common Elaboration-model Traits:: 
* Dynamic Elaboration Model in GNAT:: 
* Static Elaboration Model in GNAT:: 
* SPARK Elaboration Model in GNAT:: 
* Legacy Elaboration Model in GNAT:: 
* Mixing Elaboration Models:: 
* Elaboration Circularities:: 
* Resolving Elaboration Circularities:: 
* Resolving Task Issues:: 
* Elaboration-related Compiler Switches:: 
* Summary of Procedures for Elaboration Control:: 
* Inspecting the Chosen Elaboration Order:: 

Inline Assembler

* Basic Assembler Syntax:: 
* A Simple Example of Inline Assembler:: 
* Output Variables in Inline Assembler:: 
* Input Variables in Inline Assembler:: 
* Inlining Inline Assembler Code:: 
* Other Asm Functionality:: 

Other Asm Functionality

* The Clobber Parameter:: 
* The Volatile Parameter:: 

@end detailmenu
@end menu

@node About This Guide,Getting Started with GNAT,Top,Top
@anchor{gnat_ugn/about_this_guide about-this-guide}@anchor{2}@anchor{gnat_ugn/about_this_guide doc}@anchor{3}@anchor{gnat_ugn/about_this_guide gnat-user-s-guide-for-native-platforms}@anchor{4}@anchor{gnat_ugn/about_this_guide id1}@anchor{5}
@chapter About This Guide



This guide describes the use of GNAT,
a compiler and software development
toolset for the full Ada programming language.
It documents the features of the compiler and tools, and explains
how to use them to build Ada applications.

GNAT implements Ada 95, Ada 2005 and Ada 2012, and it may also be
invoked in Ada 83 compatibility mode.
By default, GNAT assumes Ada 2012, but you can override with a
compiler switch (@ref{6,,Compiling Different Versions of Ada})
to explicitly specify the language version.
Throughout this manual, references to 'Ada' without a year suffix
apply to all Ada 95/2005/2012 versions of the language.

@menu
* What This Guide Contains:: 
* What You Should Know before Reading This Guide:: 
* Related Information:: 
* A Note to Readers of Previous Versions of the Manual:: 
* Conventions:: 

@end menu

@node What This Guide Contains,What You Should Know before Reading This Guide,,About This Guide
@anchor{gnat_ugn/about_this_guide what-this-guide-contains}@anchor{7}
@section What This Guide Contains


This guide contains the following chapters:


@itemize *

@item 
@ref{8,,Getting Started with GNAT} describes how to get started compiling
and running Ada programs with the GNAT Ada programming environment.

@item 
@ref{9,,The GNAT Compilation Model} describes the compilation model used
by GNAT.

@item 
@ref{a,,Building Executable Programs with GNAT} describes how to use the
main GNAT tools to build executable programs, and it also gives examples of
using the GNU make utility with GNAT.

@item 
@ref{b,,GNAT Utility Programs} explains the various utility programs that
are included in the GNAT environment

@item 
@ref{c,,GNAT and Program Execution} covers a number of topics related to
running, debugging, and tuning the performace of programs developed
with GNAT
@end itemize

Appendices cover several additional topics:


@itemize *

@item 
@ref{d,,Platform-Specific Information} describes the different run-time
library implementations and also presents information on how to use
GNAT on several specific platforms

@item 
@ref{e,,Example of Binder Output File} shows the source code for the binder
output file for a sample program.

@item 
@ref{f,,Elaboration Order Handling in GNAT} describes how GNAT helps
you deal with elaboration order issues.

@item 
@ref{10,,Inline Assembler} shows how to use the inline assembly facility
in an Ada program.
@end itemize

@node What You Should Know before Reading This Guide,Related Information,What This Guide Contains,About This Guide
@anchor{gnat_ugn/about_this_guide what-you-should-know-before-reading-this-guide}@anchor{11}
@section What You Should Know before Reading This Guide


@geindex Ada 95 Language Reference Manual

@geindex Ada 2005 Language Reference Manual

This guide assumes a basic familiarity with the Ada 95 language, as
described in the International Standard ANSI/ISO/IEC-8652:1995, January
1995.
It does not require knowledge of the features introduced by Ada 2005
or Ada 2012.
Reference manuals for Ada 95, Ada 2005, and Ada 2012 are included in
the GNAT documentation package.

@node Related Information,A Note to Readers of Previous Versions of the Manual,What You Should Know before Reading This Guide,About This Guide
@anchor{gnat_ugn/about_this_guide related-information}@anchor{12}
@section Related Information


For further information about Ada and related tools, please refer to the
following documents:


@itemize *

@item 
@cite{Ada 95 Reference Manual}, @cite{Ada 2005 Reference Manual}, and
@cite{Ada 2012 Reference Manual}, which contain reference
material for the several revisions of the Ada language standard.

@item 
@cite{GNAT Reference_Manual}, which contains all reference material for the GNAT
implementation of Ada.

@item 
@cite{Using the GNAT Programming Studio}, which describes the GPS
Integrated Development Environment.

@item 
@cite{GNAT Programming Studio Tutorial}, which introduces the
main GPS features through examples.

@item 
@cite{Debugging with GDB},
for all details on the use of the GNU source-level debugger.

@item 
@cite{GNU Emacs Manual},
for full information on the extensible editor and programming
environment Emacs.
@end itemize

@node A Note to Readers of Previous Versions of the Manual,Conventions,Related Information,About This Guide
@anchor{gnat_ugn/about_this_guide a-note-to-readers-of-previous-versions-of-the-manual}@anchor{13}
@section A Note to Readers of Previous Versions of the Manual


In early 2015 the GNAT manuals were transitioned to the
reStructuredText (rst) / Sphinx documentation generator technology.
During that process the @cite{GNAT User's Guide} was reorganized
so that related topics would be described together in the same chapter
or appendix.  Here's a summary of the major changes realized in
the new document structure.


@itemize *

@item 
@ref{9,,The GNAT Compilation Model} has been extended so that it now covers
the following material:


@itemize -

@item 
The @code{gnatname}, @code{gnatkr}, and @code{gnatchop} tools

@item 
@ref{14,,Configuration Pragmas}

@item 
@ref{15,,GNAT and Libraries}

@item 
@ref{16,,Conditional Compilation} including @ref{17,,Preprocessing with gnatprep}
and @ref{18,,Integrated Preprocessing}

@item 
@ref{19,,Generating Ada Bindings for C and C++ headers}

@item 
@ref{1a,,Using GNAT Files with External Tools}
@end itemize

@item 
@ref{a,,Building Executable Programs with GNAT} is a new chapter consolidating
the following content:


@itemize -

@item 
@ref{1b,,Building with gnatmake}

@item 
@ref{1c,,Compiling with gcc}

@item 
@ref{1d,,Binding with gnatbind}

@item 
@ref{1e,,Linking with gnatlink}

@item 
@ref{1f,,Using the GNU make Utility}
@end itemize

@item 
@ref{b,,GNAT Utility Programs} is a new chapter consolidating the information about several
GNAT tools:



@itemize -

@item 
@ref{20,,The File Cleanup Utility gnatclean}

@item 
@ref{21,,The GNAT Library Browser gnatls}

@item 
@ref{22,,The Cross-Referencing Tools gnatxref and gnatfind}

@item 
@ref{23,,The Ada to HTML Converter gnathtml}
@end itemize

@item 
@ref{c,,GNAT and Program Execution} is a new chapter consolidating the following:


@itemize -

@item 
@ref{24,,Running and Debugging Ada Programs}

@item 
@ref{25,,Profiling}

@item 
@ref{26,,Improving Performance}

@item 
@ref{27,,Overflow Check Handling in GNAT}

@item 
@ref{28,,Performing Dimensionality Analysis in GNAT}

@item 
@ref{29,,Stack Related Facilities}

@item 
@ref{2a,,Memory Management Issues}
@end itemize

@item 
@ref{d,,Platform-Specific Information} is a new appendix consolidating the following:


@itemize -

@item 
@ref{2b,,Run-Time Libraries}

@item 
@ref{2c,,Microsoft Windows Topics}

@item 
@ref{2d,,Mac OS Topics}
@end itemize

@item 
The @emph{Compatibility and Porting Guide} appendix has been moved to the
@cite{GNAT Reference Manual}. It now includes a section
@emph{Writing Portable Fixed-Point Declarations} which was previously
a separate chapter in the @cite{GNAT User's Guide}.
@end itemize

@node Conventions,,A Note to Readers of Previous Versions of the Manual,About This Guide
@anchor{gnat_ugn/about_this_guide conventions}@anchor{2e}
@section Conventions


@geindex Conventions
@geindex typographical

@geindex Typographical conventions

Following are examples of the typographical and graphic conventions used
in this guide:


@itemize *

@item 
@code{Functions}, @code{utility program names}, @code{standard names},
and @code{classes}.

@item 
@code{Option flags}

@item 
@code{File names}

@item 
@code{Variables}

@item 
@emph{Emphasis}

@item 
[optional information or parameters]

@item 
Examples are described by text

@example
and then shown this way.
@end example

@item 
Commands that are entered by the user are shown as preceded by a prompt string
comprising the @code{$} character followed by a space.

@item 
Full file names are shown with the '/' character
as the directory separator; e.g., @code{parent-dir/subdir/myfile.adb}.
If you are using GNAT on a Windows platform, please note that
the '\' character should be used instead.
@end itemize

@node Getting Started with GNAT,The GNAT Compilation Model,About This Guide,Top
@anchor{gnat_ugn/getting_started_with_gnat getting-started-with-gnat}@anchor{8}@anchor{gnat_ugn/getting_started_with_gnat doc}@anchor{2f}@anchor{gnat_ugn/getting_started_with_gnat id1}@anchor{30}
@chapter Getting Started with GNAT


This chapter describes how to use GNAT's command line interface to build
executable Ada programs.
On most platforms a visually oriented Integrated Development Environment
is also available, the GNAT Programming Studio (GPS).
GPS offers a graphical "look and feel", support for development in
other programming languages, comprehensive browsing features, and
many other capabilities.
For information on GPS please refer to
@cite{Using the GNAT Programming Studio}.

@menu
* Running GNAT:: 
* Running a Simple Ada Program:: 
* Running a Program with Multiple Units:: 
* Using the gnatmake Utility:: 

@end menu

@node Running GNAT,Running a Simple Ada Program,,Getting Started with GNAT
@anchor{gnat_ugn/getting_started_with_gnat running-gnat}@anchor{31}@anchor{gnat_ugn/getting_started_with_gnat id2}@anchor{32}
@section Running GNAT


Three steps are needed to create an executable file from an Ada source
file:


@itemize *

@item 
The source file(s) must be compiled.

@item 
The file(s) must be bound using the GNAT binder.

@item 
All appropriate object files must be linked to produce an executable.
@end itemize

All three steps are most commonly handled by using the @code{gnatmake}
utility program that, given the name of the main program, automatically
performs the necessary compilation, binding and linking steps.

@node Running a Simple Ada Program,Running a Program with Multiple Units,Running GNAT,Getting Started with GNAT
@anchor{gnat_ugn/getting_started_with_gnat running-a-simple-ada-program}@anchor{33}@anchor{gnat_ugn/getting_started_with_gnat id3}@anchor{34}
@section Running a Simple Ada Program


Any text editor may be used to prepare an Ada program.
(If Emacs is used, the optional Ada mode may be helpful in laying out the
program.)
The program text is a normal text file. We will assume in our initial
example that you have used your editor to prepare the following
standard format text file:

@example
with Ada.Text_IO; use Ada.Text_IO;
procedure Hello is
begin
   Put_Line ("Hello WORLD!");
end Hello;
@end example

This file should be named @code{hello.adb}.
With the normal default file naming conventions, GNAT requires
that each file
contain a single compilation unit whose file name is the
unit name,
with periods replaced by hyphens; the
extension is @code{ads} for a
spec and @code{adb} for a body.
You can override this default file naming convention by use of the
special pragma @code{Source_File_Name} (for further information please
see @ref{35,,Using Other File Names}).
Alternatively, if you want to rename your files according to this default
convention, which is probably more convenient if you will be using GNAT
for all your compilations, then the @code{gnatchop} utility
can be used to generate correctly-named source files
(see @ref{36,,Renaming Files with gnatchop}).

You can compile the program using the following command (@code{$} is used
as the command prompt in the examples in this document):

@example
$ gcc -c hello.adb
@end example

@code{gcc} is the command used to run the compiler. This compiler is
capable of compiling programs in several languages, including Ada and
C. It assumes that you have given it an Ada program if the file extension is
either @code{.ads} or @code{.adb}, and it will then call
the GNAT compiler to compile the specified file.

The @code{-c} switch is required. It tells @code{gcc} to only do a
compilation. (For C programs, @code{gcc} can also do linking, but this
capability is not used directly for Ada programs, so the @code{-c}
switch must always be present.)

This compile command generates a file
@code{hello.o}, which is the object
file corresponding to your Ada program. It also generates
an 'Ada Library Information' file @code{hello.ali},
which contains additional information used to check
that an Ada program is consistent.
To build an executable file,
use @code{gnatbind} to bind the program
and @code{gnatlink} to link it. The
argument to both @code{gnatbind} and @code{gnatlink} is the name of the
@code{ALI} file, but the default extension of @code{.ali} can
be omitted. This means that in the most common case, the argument
is simply the name of the main program:

@example
$ gnatbind hello
$ gnatlink hello
@end example

A simpler method of carrying out these steps is to use @code{gnatmake},
a master program that invokes all the required
compilation, binding and linking tools in the correct order. In particular,
@code{gnatmake} automatically recompiles any sources that have been
modified since they were last compiled, or sources that depend
on such modified sources, so that 'version skew' is avoided.

@geindex Version skew (avoided by `@w{`}gnatmake`@w{`})

@example
$ gnatmake hello.adb
@end example

The result is an executable program called @code{hello}, which can be
run by entering:

@example
$ hello
@end example

assuming that the current directory is on the search path
for executable programs.

and, if all has gone well, you will see:

@example
Hello WORLD!
@end example

appear in response to this command.

@node Running a Program with Multiple Units,Using the gnatmake Utility,Running a Simple Ada Program,Getting Started with GNAT
@anchor{gnat_ugn/getting_started_with_gnat id4}@anchor{37}@anchor{gnat_ugn/getting_started_with_gnat running-a-program-with-multiple-units}@anchor{38}
@section Running a Program with Multiple Units


Consider a slightly more complicated example that has three files: a
main program, and the spec and body of a package:

@example
package Greetings is
   procedure Hello;
   procedure Goodbye;
end Greetings;

with Ada.Text_IO; use Ada.Text_IO;
package body Greetings is
   procedure Hello is
   begin
      Put_Line ("Hello WORLD!");
   end Hello;

   procedure Goodbye is
   begin
      Put_Line ("Goodbye WORLD!");
   end Goodbye;
end Greetings;

with Greetings;
procedure Gmain is
begin
   Greetings.Hello;
   Greetings.Goodbye;
end Gmain;
@end example

Following the one-unit-per-file rule, place this program in the
following three separate files:


@table @asis

@item @emph{greetings.ads}

spec of package @code{Greetings}

@item @emph{greetings.adb}

body of package @code{Greetings}

@item @emph{gmain.adb}

body of main program
@end table

To build an executable version of
this program, we could use four separate steps to compile, bind, and link
the program, as follows:

@example
$ gcc -c gmain.adb
$ gcc -c greetings.adb
$ gnatbind gmain
$ gnatlink gmain
@end example

Note that there is no required order of compilation when using GNAT.
In particular it is perfectly fine to compile the main program first.
Also, it is not necessary to compile package specs in the case where
there is an accompanying body; you only need to compile the body. If you want
to submit these files to the compiler for semantic checking and not code
generation, then use the @code{-gnatc} switch:

@example
$ gcc -c greetings.ads -gnatc
@end example

Although the compilation can be done in separate steps as in the
above example, in practice it is almost always more convenient
to use the @code{gnatmake} tool. All you need to know in this case
is the name of the main program's source file. The effect of the above four
commands can be achieved with a single one:

@example
$ gnatmake gmain.adb
@end example

In the next section we discuss the advantages of using @code{gnatmake} in
more detail.

@node Using the gnatmake Utility,,Running a Program with Multiple Units,Getting Started with GNAT
@anchor{gnat_ugn/getting_started_with_gnat using-the-gnatmake-utility}@anchor{39}@anchor{gnat_ugn/getting_started_with_gnat id5}@anchor{3a}
@section Using the @code{gnatmake} Utility


If you work on a program by compiling single components at a time using
@code{gcc}, you typically keep track of the units you modify. In order to
build a consistent system, you compile not only these units, but also any
units that depend on the units you have modified.
For example, in the preceding case,
if you edit @code{gmain.adb}, you only need to recompile that file. But if
you edit @code{greetings.ads}, you must recompile both
@code{greetings.adb} and @code{gmain.adb}, because both files contain
units that depend on @code{greetings.ads}.

@code{gnatbind} will warn you if you forget one of these compilation
steps, so that it is impossible to generate an inconsistent program as a
result of forgetting to do a compilation. Nevertheless it is tedious and
error-prone to keep track of dependencies among units.
One approach to handle the dependency-bookkeeping is to use a
makefile. However, makefiles present maintenance problems of their own:
if the dependencies change as you change the program, you must make
sure that the makefile is kept up-to-date manually, which is also an
error-prone process.

The @code{gnatmake} utility takes care of these details automatically.
Invoke it using either one of the following forms:

@example
$ gnatmake gmain.adb
$ gnatmake gmain
@end example

The argument is the name of the file containing the main program;
you may omit the extension. @code{gnatmake}
examines the environment, automatically recompiles any files that need
recompiling, and binds and links the resulting set of object files,
generating the executable file, @code{gmain}.
In a large program, it
can be extremely helpful to use @code{gnatmake}, because working out by hand
what needs to be recompiled can be difficult.

Note that @code{gnatmake} takes into account all the Ada rules that
establish dependencies among units. These include dependencies that result
from inlining subprogram bodies, and from
generic instantiation. Unlike some other
Ada make tools, @code{gnatmake} does not rely on the dependencies that were
found by the compiler on a previous compilation, which may possibly
be wrong when sources change. @code{gnatmake} determines the exact set of
dependencies from scratch each time it is run.

@c -- Example: A |withing| unit has a |with| clause, it |withs| a |withed| unit

@node The GNAT Compilation Model,Building Executable Programs with GNAT,Getting Started with GNAT,Top
@anchor{gnat_ugn/the_gnat_compilation_model doc}@anchor{3b}@anchor{gnat_ugn/the_gnat_compilation_model the-gnat-compilation-model}@anchor{9}@anchor{gnat_ugn/the_gnat_compilation_model id1}@anchor{3c}
@chapter The GNAT Compilation Model


@geindex GNAT compilation model

@geindex Compilation model

This chapter describes the compilation model used by GNAT. Although
similar to that used by other languages such as C and C++, this model
is substantially different from the traditional Ada compilation models,
which are based on a centralized program library. The chapter covers
the following material:


@itemize *

@item 
Topics related to source file makeup and naming


@itemize *

@item 
@ref{3d,,Source Representation}

@item 
@ref{3e,,Foreign Language Representation}

@item 
@ref{3f,,File Naming Topics and Utilities}
@end itemize

@item 
@ref{14,,Configuration Pragmas}

@item 
@ref{40,,Generating Object Files}

@item 
@ref{41,,Source Dependencies}

@item 
@ref{42,,The Ada Library Information Files}

@item 
@ref{43,,Binding an Ada Program}

@item 
@ref{15,,GNAT and Libraries}

@item 
@ref{16,,Conditional Compilation}

@item 
@ref{44,,Mixed Language Programming}

@item 
@ref{45,,GNAT and Other Compilation Models}

@item 
@ref{1a,,Using GNAT Files with External Tools}
@end itemize

@menu
* Source Representation:: 
* Foreign Language Representation:: 
* File Naming Topics and Utilities:: 
* Configuration Pragmas:: 
* Generating Object Files:: 
* Source Dependencies:: 
* The Ada Library Information Files:: 
* Binding an Ada Program:: 
* GNAT and Libraries:: 
* Conditional Compilation:: 
* Mixed Language Programming:: 
* GNAT and Other Compilation Models:: 
* Using GNAT Files with External Tools:: 

@end menu

@node Source Representation,Foreign Language Representation,,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model source-representation}@anchor{3d}@anchor{gnat_ugn/the_gnat_compilation_model id2}@anchor{46}
@section Source Representation


@geindex Latin-1

@geindex VT
@geindex HT
@geindex CR
@geindex LF
@geindex FF

Ada source programs are represented in standard text files, using
Latin-1 coding. Latin-1 is an 8-bit code that includes the familiar
7-bit ASCII set, plus additional characters used for
representing foreign languages (see @ref{3e,,Foreign Language Representation}
for support of non-USA character sets). The format effector characters
are represented using their standard ASCII encodings, as follows:

@quotation


@multitable {xxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxx} 
@item

Character

@tab

Effect

@tab

Code

@item

@code{VT}

@tab

Vertical tab

@tab

@code{16#0B#}

@item

@code{HT}

@tab

Horizontal tab

@tab

@code{16#09#}

@item

@code{CR}

@tab

Carriage return

@tab

@code{16#0D#}

@item

@code{LF}

@tab

Line feed

@tab

@code{16#0A#}

@item

@code{FF}

@tab

Form feed

@tab

@code{16#0C#}

@end multitable

@end quotation

Source files are in standard text file format. In addition, GNAT will
recognize a wide variety of stream formats, in which the end of
physical lines is marked by any of the following sequences:
@code{LF}, @code{CR}, @code{CR-LF}, or @code{LF-CR}. This is useful
in accommodating files that are imported from other operating systems.

@geindex End of source file; Source file@comma{} end

@geindex SUB (control character)

The end of a source file is normally represented by the physical end of
file. However, the control character @code{16#1A#} (@code{SUB}) is also
recognized as signalling the end of the source file. Again, this is
provided for compatibility with other operating systems where this
code is used to represent the end of file.

@geindex spec (definition)
@geindex compilation (definition)

Each file contains a single Ada compilation unit, including any pragmas
associated with the unit. For example, this means you must place a
package declaration (a package @emph{spec}) and the corresponding body in
separate files. An Ada @emph{compilation} (which is a sequence of
compilation units) is represented using a sequence of files. Similarly,
you will place each subunit or child unit in a separate file.

@node Foreign Language Representation,File Naming Topics and Utilities,Source Representation,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model foreign-language-representation}@anchor{3e}@anchor{gnat_ugn/the_gnat_compilation_model id3}@anchor{47}
@section Foreign Language Representation


GNAT supports the standard character sets defined in Ada as well as
several other non-standard character sets for use in localized versions
of the compiler (@ref{48,,Character Set Control}).

@menu
* Latin-1:: 
* Other 8-Bit Codes:: 
* Wide_Character Encodings:: 
* Wide_Wide_Character Encodings:: 

@end menu

@node Latin-1,Other 8-Bit Codes,,Foreign Language Representation
@anchor{gnat_ugn/the_gnat_compilation_model id4}@anchor{49}@anchor{gnat_ugn/the_gnat_compilation_model latin-1}@anchor{4a}
@subsection Latin-1


@geindex Latin-1

The basic character set is Latin-1. This character set is defined by ISO
standard 8859, part 1. The lower half (character codes @code{16#00#}
... @code{16#7F#)} is identical to standard ASCII coding, but the upper
half is used to represent additional characters. These include extended letters
used by European languages, such as French accents, the vowels with umlauts
used in German, and the extra letter A-ring used in Swedish.

@geindex Ada.Characters.Latin_1

For a complete list of Latin-1 codes and their encodings, see the source
file of library unit @code{Ada.Characters.Latin_1} in file
@code{a-chlat1.ads}.
You may use any of these extended characters freely in character or
string literals. In addition, the extended characters that represent
letters can be used in identifiers.

@node Other 8-Bit Codes,Wide_Character Encodings,Latin-1,Foreign Language Representation
@anchor{gnat_ugn/the_gnat_compilation_model other-8-bit-codes}@anchor{4b}@anchor{gnat_ugn/the_gnat_compilation_model id5}@anchor{4c}
@subsection Other 8-Bit Codes


GNAT also supports several other 8-bit coding schemes:

@geindex Latin-2

@geindex ISO 8859-2


@table @asis

@item @emph{ISO 8859-2 (Latin-2)}

Latin-2 letters allowed in identifiers, with uppercase and lowercase
equivalence.
@end table

@geindex Latin-3

@geindex ISO 8859-3


@table @asis

@item @emph{ISO 8859-3 (Latin-3)}

Latin-3 letters allowed in identifiers, with uppercase and lowercase
equivalence.
@end table

@geindex Latin-4

@geindex ISO 8859-4


@table @asis

@item @emph{ISO 8859-4 (Latin-4)}

Latin-4 letters allowed in identifiers, with uppercase and lowercase
equivalence.
@end table

@geindex ISO 8859-5

@geindex Cyrillic


@table @asis

@item @emph{ISO 8859-5 (Cyrillic)}

ISO 8859-5 letters (Cyrillic) allowed in identifiers, with uppercase and
lowercase equivalence.
@end table

@geindex ISO 8859-15

@geindex Latin-9


@table @asis

@item @emph{ISO 8859-15 (Latin-9)}

ISO 8859-15 (Latin-9) letters allowed in identifiers, with uppercase and
lowercase equivalence
@end table

@geindex code page 437 (IBM PC)


@table @asis

@item @emph{IBM PC (code page 437)}

This code page is the normal default for PCs in the U.S. It corresponds
to the original IBM PC character set. This set has some, but not all, of
the extended Latin-1 letters, but these letters do not have the same
encoding as Latin-1. In this mode, these letters are allowed in
identifiers with uppercase and lowercase equivalence.
@end table

@geindex code page 850 (IBM PC)


@table @asis

@item @emph{IBM PC (code page 850)}

This code page is a modification of 437 extended to include all the
Latin-1 letters, but still not with the usual Latin-1 encoding. In this
mode, all these letters are allowed in identifiers with uppercase and
lowercase equivalence.

@item @emph{Full Upper 8-bit}

Any character in the range 80-FF allowed in identifiers, and all are
considered distinct. In other words, there are no uppercase and lowercase
equivalences in this range. This is useful in conjunction with
certain encoding schemes used for some foreign character sets (e.g.,
the typical method of representing Chinese characters on the PC).

@item @emph{No Upper-Half}

No upper-half characters in the range 80-FF are allowed in identifiers.
This gives Ada 83 compatibility for identifier names.
@end table

For precise data on the encodings permitted, and the uppercase and lowercase
equivalences that are recognized, see the file @code{csets.adb} in
the GNAT compiler sources. You will need to obtain a full source release
of GNAT to obtain this file.

@node Wide_Character Encodings,Wide_Wide_Character Encodings,Other 8-Bit Codes,Foreign Language Representation
@anchor{gnat_ugn/the_gnat_compilation_model id6}@anchor{4d}@anchor{gnat_ugn/the_gnat_compilation_model wide-character-encodings}@anchor{4e}
@subsection Wide_Character Encodings


GNAT allows wide character codes to appear in character and string
literals, and also optionally in identifiers, by means of the following
possible encoding schemes:


@table @asis

@item @emph{Hex Coding}

In this encoding, a wide character is represented by the following five
character sequence:

@example
ESC a b c d
@end example

where @code{a}, @code{b}, @code{c}, @code{d} are the four hexadecimal
characters (using uppercase letters) of the wide character code. For
example, ESC A345 is used to represent the wide character with code
@code{16#A345#}.
This scheme is compatible with use of the full Wide_Character set.

@item @emph{Upper-Half Coding}

@geindex Upper-Half Coding

The wide character with encoding @code{16#abcd#} where the upper bit is on
(in other words, 'a' is in the range 8-F) is represented as two bytes,
@code{16#ab#} and @code{16#cd#}. The second byte cannot be a format control
character, but is not required to be in the upper half. This method can
be also used for shift-JIS or EUC, where the internal coding matches the
external coding.

@item @emph{Shift JIS Coding}

@geindex Shift JIS Coding

A wide character is represented by a two-character sequence,
@code{16#ab#} and
@code{16#cd#}, with the restrictions described for upper-half encoding as
described above. The internal character code is the corresponding JIS
character according to the standard algorithm for Shift-JIS
conversion. Only characters defined in the JIS code set table can be
used with this encoding method.

@item @emph{EUC Coding}

@geindex EUC Coding

A wide character is represented by a two-character sequence
@code{16#ab#} and
@code{16#cd#}, with both characters being in the upper half. The internal
character code is the corresponding JIS character according to the EUC
encoding algorithm. Only characters defined in the JIS code set table
can be used with this encoding method.

@item @emph{UTF-8 Coding}

A wide character is represented using
UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
10646-1/Am.2. Depending on the character value, the representation
is a one, two, or three byte sequence:

@example
16#0000#-16#007f#: 2#0xxxxxxx#
16#0080#-16#07ff#: 2#110xxxxx# 2#10xxxxxx#
16#0800#-16#ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#
@end example

where the @code{xxx} bits correspond to the left-padded bits of the
16-bit character value. Note that all lower half ASCII characters
are represented as ASCII bytes and all upper half characters and
other wide characters are represented as sequences of upper-half
(The full UTF-8 scheme allows for encoding 31-bit characters as
6-byte sequences, and in the following section on wide wide
characters, the use of these sequences is documented).

@item @emph{Brackets Coding}

In this encoding, a wide character is represented by the following eight
character sequence:

@example
[ " a b c d " ]
@end example

where @code{a}, @code{b}, @code{c}, @code{d} are the four hexadecimal
characters (using uppercase letters) of the wide character code. For
example, ['A345'] is used to represent the wide character with code
@code{16#A345#}. It is also possible (though not required) to use the
Brackets coding for upper half characters. For example, the code
@code{16#A3#} can be represented as @code{['A3']}.

This scheme is compatible with use of the full Wide_Character set,
and is also the method used for wide character encoding in some standard
ACATS (Ada Conformity Assessment Test Suite) test suite distributions.
@end table

@cartouche
@quotation Note 
Some of these coding schemes do not permit the full use of the
Ada character set. For example, neither Shift JIS nor EUC allow the
use of the upper half of the Latin-1 set.
@end quotation
@end cartouche

@node Wide_Wide_Character Encodings,,Wide_Character Encodings,Foreign Language Representation
@anchor{gnat_ugn/the_gnat_compilation_model id7}@anchor{4f}@anchor{gnat_ugn/the_gnat_compilation_model wide-wide-character-encodings}@anchor{50}
@subsection Wide_Wide_Character Encodings


GNAT allows wide wide character codes to appear in character and string
literals, and also optionally in identifiers, by means of the following
possible encoding schemes:


@table @asis

@item @emph{UTF-8 Coding}

A wide character is represented using
UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
10646-1/Am.2. Depending on the character value, the representation
of character codes with values greater than 16#FFFF# is a
is a four, five, or six byte sequence:

@example
16#01_0000#-16#10_FFFF#:     11110xxx 10xxxxxx 10xxxxxx
                             10xxxxxx
16#0020_0000#-16#03FF_FFFF#: 111110xx 10xxxxxx 10xxxxxx
                             10xxxxxx 10xxxxxx
16#0400_0000#-16#7FFF_FFFF#: 1111110x 10xxxxxx 10xxxxxx
                             10xxxxxx 10xxxxxx 10xxxxxx
@end example

where the @code{xxx} bits correspond to the left-padded bits of the
32-bit character value.

@item @emph{Brackets Coding}

In this encoding, a wide wide character is represented by the following ten or
twelve byte character sequence:

@example
[ " a b c d e f " ]
[ " a b c d e f g h " ]
@end example

where @code{a-h} are the six or eight hexadecimal
characters (using uppercase letters) of the wide wide character code. For
example, ["1F4567"] is used to represent the wide wide character with code
@code{16#001F_4567#}.

This scheme is compatible with use of the full Wide_Wide_Character set,
and is also the method used for wide wide character encoding in some standard
ACATS (Ada Conformity Assessment Test Suite) test suite distributions.
@end table

@node File Naming Topics and Utilities,Configuration Pragmas,Foreign Language Representation,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model id8}@anchor{51}@anchor{gnat_ugn/the_gnat_compilation_model file-naming-topics-and-utilities}@anchor{3f}
@section File Naming Topics and Utilities


GNAT has a default file naming scheme and also provides the user with
a high degree of control over how the names and extensions of the
source files correspond to the Ada compilation units that they contain.

@menu
* File Naming Rules:: 
* Using Other File Names:: 
* Alternative File Naming Schemes:: 
* Handling Arbitrary File Naming Conventions with gnatname:: 
* File Name Krunching with gnatkr:: 
* Renaming Files with gnatchop:: 

@end menu

@node File Naming Rules,Using Other File Names,,File Naming Topics and Utilities
@anchor{gnat_ugn/the_gnat_compilation_model file-naming-rules}@anchor{52}@anchor{gnat_ugn/the_gnat_compilation_model id9}@anchor{53}
@subsection File Naming Rules


The default file name is determined by the name of the unit that the
file contains. The name is formed by taking the full expanded name of
the unit and replacing the separating dots with hyphens and using
lowercase for all letters.

An exception arises if the file name generated by the above rules starts
with one of the characters
@code{a}, @code{g}, @code{i}, or @code{s}, and the second character is a
minus. In this case, the character tilde is used in place
of the minus. The reason for this special rule is to avoid clashes with
the standard names for child units of the packages System, Ada,
Interfaces, and GNAT, which use the prefixes
@code{s-}, @code{a-}, @code{i-}, and @code{g-},
respectively.

The file extension is @code{.ads} for a spec and
@code{.adb} for a body. The following table shows some
examples of these rules.

@quotation


@multitable {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} 
@item

Source File

@tab

Ada Compilation Unit

@item

@code{main.ads}

@tab

Main (spec)

@item

@code{main.adb}

@tab

Main (body)

@item

@code{arith_functions.ads}

@tab

Arith_Functions (package spec)

@item

@code{arith_functions.adb}

@tab

Arith_Functions (package body)

@item

@code{func-spec.ads}

@tab

Func.Spec (child package spec)

@item

@code{func-spec.adb}

@tab

Func.Spec (child package body)

@item

@code{main-sub.adb}

@tab

Sub (subunit of Main)

@item

@code{a~bad.adb}

@tab

A.Bad (child package body)

@end multitable

@end quotation

Following these rules can result in excessively long
file names if corresponding
unit names are long (for example, if child units or subunits are
heavily nested). An option is available to shorten such long file names
(called file name 'krunching'). This may be particularly useful when
programs being developed with GNAT are to be used on operating systems
with limited file name lengths. @ref{54,,Using gnatkr}.

Of course, no file shortening algorithm can guarantee uniqueness over
all possible unit names; if file name krunching is used, it is your
responsibility to ensure no name clashes occur. Alternatively you
can specify the exact file names that you want used, as described
in the next section. Finally, if your Ada programs are migrating from a
compiler with a different naming convention, you can use the gnatchop
utility to produce source files that follow the GNAT naming conventions.
(For details see @ref{36,,Renaming Files with gnatchop}.)

Note: in the case of Windows or Mac OS operating systems, case is not
significant. So for example on Windows if the canonical name is
@code{main-sub.adb}, you can use the file name @code{Main-Sub.adb} instead.
However, case is significant for other operating systems, so for example,
if you want to use other than canonically cased file names on a Unix system,
you need to follow the procedures described in the next section.

@node Using Other File Names,Alternative File Naming Schemes,File Naming Rules,File Naming Topics and Utilities
@anchor{gnat_ugn/the_gnat_compilation_model id10}@anchor{55}@anchor{gnat_ugn/the_gnat_compilation_model using-other-file-names}@anchor{35}
@subsection Using Other File Names


@geindex File names

In the previous section, we have described the default rules used by
GNAT to determine the file name in which a given unit resides. It is
often convenient to follow these default rules, and if you follow them,
the compiler knows without being explicitly told where to find all
the files it needs.

@geindex Source_File_Name pragma

However, in some cases, particularly when a program is imported from
another Ada compiler environment, it may be more convenient for the
programmer to specify which file names contain which units. GNAT allows
arbitrary file names to be used by means of the Source_File_Name pragma.
The form of this pragma is as shown in the following examples:

@example
pragma Source_File_Name (My_Utilities.Stacks,
  Spec_File_Name => "myutilst_a.ada");
pragma Source_File_name (My_Utilities.Stacks,
  Body_File_Name => "myutilst.ada");
@end example

As shown in this example, the first argument for the pragma is the unit
name (in this example a child unit). The second argument has the form
of a named association. The identifier
indicates whether the file name is for a spec or a body;
the file name itself is given by a string literal.

The source file name pragma is a configuration pragma, which means that
normally it will be placed in the @code{gnat.adc}
file used to hold configuration
pragmas that apply to a complete compilation environment.
For more details on how the @code{gnat.adc} file is created and used
see @ref{56,,Handling of Configuration Pragmas}.

@geindex gnat.adc

GNAT allows completely arbitrary file names to be specified using the
source file name pragma. However, if the file name specified has an
extension other than @code{.ads} or @code{.adb} it is necessary to use
a special syntax when compiling the file. The name in this case must be
preceded by the special sequence @code{-x} followed by a space and the name
of the language, here @code{ada}, as in:

@example
$ gcc -c -x ada peculiar_file_name.sim
@end example

@code{gnatmake} handles non-standard file names in the usual manner (the
non-standard file name for the main program is simply used as the
argument to gnatmake). Note that if the extension is also non-standard,
then it must be included in the @code{gnatmake} command, it may not
be omitted.

@node Alternative File Naming Schemes,Handling Arbitrary File Naming Conventions with gnatname,Using Other File Names,File Naming Topics and Utilities
@anchor{gnat_ugn/the_gnat_compilation_model id11}@anchor{57}@anchor{gnat_ugn/the_gnat_compilation_model alternative-file-naming-schemes}@anchor{58}
@subsection Alternative File Naming Schemes


@geindex File naming schemes
@geindex alternative

@geindex File names

The previous section described the use of the @code{Source_File_Name}
pragma to allow arbitrary names to be assigned to individual source files.
However, this approach requires one pragma for each file, and especially in
large systems can result in very long @code{gnat.adc} files, and also create
a maintenance problem.

@geindex Source_File_Name pragma

GNAT also provides a facility for specifying systematic file naming schemes
other than the standard default naming scheme previously described. An
alternative scheme for naming is specified by the use of
@code{Source_File_Name} pragmas having the following format:

@example
pragma Source_File_Name (
   Spec_File_Name  => FILE_NAME_PATTERN
 [ , Casing          => CASING_SPEC]
 [ , Dot_Replacement => STRING_LITERAL ] );

pragma Source_File_Name (
   Body_File_Name  => FILE_NAME_PATTERN
 [ , Casing          => CASING_SPEC ]
 [ , Dot_Replacement => STRING_LITERAL ] ) ;

pragma Source_File_Name (
   Subunit_File_Name  => FILE_NAME_PATTERN
 [ , Casing          => CASING_SPEC ]
 [ , Dot_Replacement => STRING_LITERAL ] ) ;

FILE_NAME_PATTERN ::= STRING_LITERAL
CASING_SPEC ::= Lowercase | Uppercase | Mixedcase
@end example

The @code{FILE_NAME_PATTERN} string shows how the file name is constructed.
It contains a single asterisk character, and the unit name is substituted
systematically for this asterisk. The optional parameter
@code{Casing} indicates
whether the unit name is to be all upper-case letters, all lower-case letters,
or mixed-case. If no
@code{Casing} parameter is used, then the default is all
lower-case.

The optional @code{Dot_Replacement} string is used to replace any periods
that occur in subunit or child unit names. If no @code{Dot_Replacement}
argument is used then separating dots appear unchanged in the resulting
file name.
Although the above syntax indicates that the
@code{Casing} argument must appear
before the @code{Dot_Replacement} argument, but it
is also permissible to write these arguments in the opposite order.

As indicated, it is possible to specify different naming schemes for
bodies, specs, and subunits. Quite often the rule for subunits is the
same as the rule for bodies, in which case, there is no need to give
a separate @code{Subunit_File_Name} rule, and in this case the
@code{Body_File_name} rule is used for subunits as well.

The separate rule for subunits can also be used to implement the rather
unusual case of a compilation environment (e.g., a single directory) which
contains a subunit and a child unit with the same unit name. Although
both units cannot appear in the same partition, the Ada Reference Manual
allows (but does not require) the possibility of the two units coexisting
in the same environment.

The file name translation works in the following steps:


@itemize *

@item 
If there is a specific @code{Source_File_Name} pragma for the given unit,
then this is always used, and any general pattern rules are ignored.

@item 
If there is a pattern type @code{Source_File_Name} pragma that applies to
the unit, then the resulting file name will be used if the file exists. If
more than one pattern matches, the latest one will be tried first, and the
first attempt resulting in a reference to a file that exists will be used.

@item 
If no pattern type @code{Source_File_Name} pragma that applies to the unit
for which the corresponding file exists, then the standard GNAT default
naming rules are used.
@end itemize

As an example of the use of this mechanism, consider a commonly used scheme
in which file names are all lower case, with separating periods copied
unchanged to the resulting file name, and specs end with @code{.1.ada}, and
bodies end with @code{.2.ada}. GNAT will follow this scheme if the following
two pragmas appear:

@example
pragma Source_File_Name
  (Spec_File_Name => ".1.ada");
pragma Source_File_Name
  (Body_File_Name => ".2.ada");
@end example

The default GNAT scheme is actually implemented by providing the following
default pragmas internally:

@example
pragma Source_File_Name
  (Spec_File_Name => ".ads", Dot_Replacement => "-");
pragma Source_File_Name
  (Body_File_Name => ".adb", Dot_Replacement => "-");
@end example

Our final example implements a scheme typically used with one of the
Ada 83 compilers, where the separator character for subunits was '__'
(two underscores), specs were identified by adding @code{_.ADA}, bodies
by adding @code{.ADA}, and subunits by
adding @code{.SEP}. All file names were
upper case. Child units were not present of course since this was an
Ada 83 compiler, but it seems reasonable to extend this scheme to use
the same double underscore separator for child units.

@example
pragma Source_File_Name
  (Spec_File_Name => "_.ADA",
   Dot_Replacement => "__",
   Casing = Uppercase);
pragma Source_File_Name
  (Body_File_Name => ".ADA",
   Dot_Replacement => "__",
   Casing = Uppercase);
pragma Source_File_Name
  (Subunit_File_Name => ".SEP",
   Dot_Replacement => "__",
   Casing = Uppercase);
@end example

@geindex gnatname

@node Handling Arbitrary File Naming Conventions with gnatname,File Name Krunching with gnatkr,Alternative File Naming Schemes,File Naming Topics and Utilities
@anchor{gnat_ugn/the_gnat_compilation_model handling-arbitrary-file-naming-conventions-with-gnatname}@anchor{59}@anchor{gnat_ugn/the_gnat_compilation_model id12}@anchor{5a}
@subsection Handling Arbitrary File Naming Conventions with @code{gnatname}


@geindex File Naming Conventions

@menu
* Arbitrary File Naming Conventions:: 
* Running gnatname:: 
* Switches for gnatname:: 
* Examples of gnatname Usage:: 

@end menu

@node Arbitrary File Naming Conventions,Running gnatname,,Handling Arbitrary File Naming Conventions with gnatname
@anchor{gnat_ugn/the_gnat_compilation_model arbitrary-file-naming-conventions}@anchor{5b}@anchor{gnat_ugn/the_gnat_compilation_model id13}@anchor{5c}
@subsubsection Arbitrary File Naming Conventions


The GNAT compiler must be able to know the source file name of a compilation
unit.  When using the standard GNAT default file naming conventions
(@code{.ads} for specs, @code{.adb} for bodies), the GNAT compiler
does not need additional information.

When the source file names do not follow the standard GNAT default file naming
conventions, the GNAT compiler must be given additional information through
a configuration pragmas file (@ref{14,,Configuration Pragmas})
or a project file.
When the non-standard file naming conventions are well-defined,
a small number of pragmas @code{Source_File_Name} specifying a naming pattern
(@ref{58,,Alternative File Naming Schemes}) may be sufficient. However,
if the file naming conventions are irregular or arbitrary, a number
of pragma @code{Source_File_Name} for individual compilation units
must be defined.
To help maintain the correspondence between compilation unit names and
source file names within the compiler,
GNAT provides a tool @code{gnatname} to generate the required pragmas for a
set of files.

@node Running gnatname,Switches for gnatname,Arbitrary File Naming Conventions,Handling Arbitrary File Naming Conventions with gnatname
@anchor{gnat_ugn/the_gnat_compilation_model running-gnatname}@anchor{5d}@anchor{gnat_ugn/the_gnat_compilation_model id14}@anchor{5e}
@subsubsection Running @code{gnatname}


The usual form of the @code{gnatname} command is:

@example
$ gnatname [ switches ]  naming_pattern  [ naming_patterns ]
    [--and [ switches ]  naming_pattern  [ naming_patterns ]]
@end example

All of the arguments are optional. If invoked without any argument,
@code{gnatname} will display its usage.

When used with at least one naming pattern, @code{gnatname} will attempt to
find all the compilation units in files that follow at least one of the
naming patterns. To find these compilation units,
@code{gnatname} will use the GNAT compiler in syntax-check-only mode on all
regular files.

One or several Naming Patterns may be given as arguments to @code{gnatname}.
Each Naming Pattern is enclosed between double quotes (or single
quotes on Windows).
A Naming Pattern is a regular expression similar to the wildcard patterns
used in file names by the Unix shells or the DOS prompt.

@code{gnatname} may be called with several sections of directories/patterns.
Sections are separated by the switch @code{--and}. In each section, there must be
at least one pattern. If no directory is specified in a section, the current
directory (or the project directory if @code{-P} is used) is implied.
The options other that the directory switches and the patterns apply globally
even if they are in different sections.

Examples of Naming Patterns are:

@example
"*.[12].ada"
"*.ad[sb]*"
"body_*"    "spec_*"
@end example

For a more complete description of the syntax of Naming Patterns,
see the second kind of regular expressions described in @code{g-regexp.ads}
(the 'Glob' regular expressions).

When invoked without the switch @code{-P}, @code{gnatname} will create a
configuration pragmas file @code{gnat.adc} in the current working directory,
with pragmas @code{Source_File_Name} for each file that contains a valid Ada
unit.

@node Switches for gnatname,Examples of gnatname Usage,Running gnatname,Handling Arbitrary File Naming Conventions with gnatname
@anchor{gnat_ugn/the_gnat_compilation_model id15}@anchor{5f}@anchor{gnat_ugn/the_gnat_compilation_model switches-for-gnatname}@anchor{60}
@subsubsection Switches for @code{gnatname}


Switches for @code{gnatname} must precede any specified Naming Pattern.

You may specify any of the following switches to @code{gnatname}:

@geindex --version (gnatname)


@table @asis

@item @code{--version}

Display Copyright and version, then exit disregarding all other options.
@end table

@geindex --help (gnatname)


@table @asis

@item @code{--help}

If @code{--version} was not used, display usage, then exit disregarding
all other options.

@item @code{--subdirs=@emph{dir}}

Real object, library or exec directories are subdirectories <dir> of the
specified ones.

@item @code{--no-backup}

Do not create a backup copy of an existing project file.

@item @code{--and}

Start another section of directories/patterns.
@end table

@geindex -c (gnatname)


@table @asis

@item @code{-c@emph{filename}}

Create a configuration pragmas file @code{filename} (instead of the default
@code{gnat.adc}).
There may be zero, one or more space between @code{-c} and
@code{filename}.
@code{filename} may include directory information. @code{filename} must be
writable. There may be only one switch @code{-c}.
When a switch @code{-c} is
specified, no switch @code{-P} may be specified (see below).
@end table

@geindex -d (gnatname)


@table @asis

@item @code{-d@emph{dir}}

Look for source files in directory @code{dir}. There may be zero, one or more
spaces between @code{-d} and @code{dir}.
@code{dir} may end with @code{/**}, that is it may be of the form
@code{root_dir/**}. In this case, the directory @code{root_dir} and all of its
subdirectories, recursively, have to be searched for sources.
When a switch @code{-d}
is specified, the current working directory will not be searched for source
files, unless it is explicitly specified with a @code{-d}
or @code{-D} switch.
Several switches @code{-d} may be specified.
If @code{dir} is a relative path, it is relative to the directory of
the configuration pragmas file specified with switch
@code{-c},
or to the directory of the project file specified with switch
@code{-P} or,
if neither switch @code{-c}
nor switch @code{-P} are specified, it is relative to the
current working directory. The directory
specified with switch @code{-d} must exist and be readable.
@end table

@geindex -D (gnatname)


@table @asis

@item @code{-D@emph{filename}}

Look for source files in all directories listed in text file @code{filename}.
There may be zero, one or more spaces between @code{-D}
and @code{filename}.
@code{filename} must be an existing, readable text file.
Each nonempty line in @code{filename} must be a directory.
Specifying switch @code{-D} is equivalent to specifying as many
switches @code{-d} as there are nonempty lines in
@code{file}.

@item @code{-eL}

Follow symbolic links when processing project files.

@geindex -f (gnatname)

@item @code{-f@emph{pattern}}

Foreign patterns. Using this switch, it is possible to add sources of languages
other than Ada to the list of sources of a project file.
It is only useful if a -P switch is used.
For example,

@example
gnatname -Pprj -f"*.c" "*.ada"
@end example

will look for Ada units in all files with the @code{.ada} extension,
and will add to the list of file for project @code{prj.gpr} the C files
with extension @code{.c}.

@geindex -h (gnatname)

@item @code{-h}

Output usage (help) information. The output is written to @code{stdout}.

@geindex -P (gnatname)

@item @code{-P@emph{proj}}

Create or update project file @code{proj}. There may be zero, one or more space
between @code{-P} and @code{proj}. @code{proj} may include directory
information. @code{proj} must be writable.
There may be only one switch @code{-P}.
When a switch @code{-P} is specified,
no switch @code{-c} may be specified.
On all platforms, except on VMS, when @code{gnatname} is invoked for an
existing project file <proj>.gpr, a backup copy of the project file is created
in the project directory with file name <proj>.gpr.saved_x. 'x' is the first
non negative number that makes this backup copy a new file.

@geindex -v (gnatname)

@item @code{-v}

Verbose mode. Output detailed explanation of behavior to @code{stdout}.
This includes name of the file written, the name of the directories to search
and, for each file in those directories whose name matches at least one of
the Naming Patterns, an indication of whether the file contains a unit,
and if so the name of the unit.
@end table

@geindex -v -v (gnatname)


@table @asis

@item @code{-v -v}

Very Verbose mode. In addition to the output produced in verbose mode,
for each file in the searched directories whose name matches none of
the Naming Patterns, an indication is given that there is no match.

@geindex -x (gnatname)

@item @code{-x@emph{pattern}}

Excluded patterns. Using this switch, it is possible to exclude some files
that would match the name patterns. For example,

@example
gnatname -x "*_nt.ada" "*.ada"
@end example

will look for Ada units in all files with the @code{.ada} extension,
except those whose names end with @code{_nt.ada}.
@end table

@node Examples of gnatname Usage,,Switches for gnatname,Handling Arbitrary File Naming Conventions with gnatname
@anchor{gnat_ugn/the_gnat_compilation_model examples-of-gnatname-usage}@anchor{61}@anchor{gnat_ugn/the_gnat_compilation_model id16}@anchor{62}
@subsubsection Examples of @code{gnatname} Usage


@example
$ gnatname -c /home/me/names.adc -d sources "[a-z]*.ada*"
@end example

In this example, the directory @code{/home/me} must already exist
and be writable. In addition, the directory
@code{/home/me/sources} (specified by
@code{-d sources}) must exist and be readable.

Note the optional spaces after @code{-c} and @code{-d}.

@example
$ gnatname -P/home/me/proj -x "*_nt_body.ada"
-dsources -dsources/plus -Dcommon_dirs.txt "body_*" "spec_*"
@end example

Note that several switches @code{-d} may be used,
even in conjunction with one or several switches
@code{-D}. Several Naming Patterns and one excluded pattern
are used in this example.

@node File Name Krunching with gnatkr,Renaming Files with gnatchop,Handling Arbitrary File Naming Conventions with gnatname,File Naming Topics and Utilities
@anchor{gnat_ugn/the_gnat_compilation_model file-name-krunching-with-gnatkr}@anchor{63}@anchor{gnat_ugn/the_gnat_compilation_model id17}@anchor{64}
@subsection File Name Krunching with @code{gnatkr}


@geindex gnatkr

This section discusses the method used by the compiler to shorten
the default file names chosen for Ada units so that they do not
exceed the maximum length permitted. It also describes the
@code{gnatkr} utility that can be used to determine the result of
applying this shortening.

@menu
* About gnatkr:: 
* Using gnatkr:: 
* Krunching Method:: 
* Examples of gnatkr Usage:: 

@end menu

@node About gnatkr,Using gnatkr,,File Name Krunching with gnatkr
@anchor{gnat_ugn/the_gnat_compilation_model id18}@anchor{65}@anchor{gnat_ugn/the_gnat_compilation_model about-gnatkr}@anchor{66}
@subsubsection About @code{gnatkr}


The default file naming rule in GNAT
is that the file name must be derived from
the unit name. The exact default rule is as follows:


@itemize *

@item 
Take the unit name and replace all dots by hyphens.

@item 
If such a replacement occurs in the
second character position of a name, and the first character is
@code{a}, @code{g}, @code{s}, or @code{i},
then replace the dot by the character
@code{~} (tilde)
instead of a minus.

The reason for this exception is to avoid clashes
with the standard names for children of System, Ada, Interfaces,
and GNAT, which use the prefixes
@code{s-}, @code{a-}, @code{i-}, and @code{g-},
respectively.
@end itemize

The @code{-gnatk@emph{nn}}
switch of the compiler activates a 'krunching'
circuit that limits file names to nn characters (where nn is a decimal
integer).

The @code{gnatkr} utility can be used to determine the krunched name for
a given file, when krunched to a specified maximum length.

@node Using gnatkr,Krunching Method,About gnatkr,File Name Krunching with gnatkr
@anchor{gnat_ugn/the_gnat_compilation_model id19}@anchor{67}@anchor{gnat_ugn/the_gnat_compilation_model using-gnatkr}@anchor{54}
@subsubsection Using @code{gnatkr}


The @code{gnatkr} command has the form:

@example
$ gnatkr name [ length ]
@end example

@code{name} is the uncrunched file name, derived from the name of the unit
in the standard manner described in the previous section (i.e., in particular
all dots are replaced by hyphens). The file name may or may not have an
extension (defined as a suffix of the form period followed by arbitrary
characters other than period). If an extension is present then it will
be preserved in the output. For example, when krunching @code{hellofile.ads}
to eight characters, the result will be hellofil.ads.

Note: for compatibility with previous versions of @code{gnatkr} dots may
appear in the name instead of hyphens, but the last dot will always be
taken as the start of an extension. So if @code{gnatkr} is given an argument
such as @code{Hello.World.adb} it will be treated exactly as if the first
period had been a hyphen, and for example krunching to eight characters
gives the result @code{hellworl.adb}.

Note that the result is always all lower case.
Characters of the other case are folded as required.

@code{length} represents the length of the krunched name. The default
when no argument is given is 8 characters. A length of zero stands for
unlimited, in other words do not chop except for system files where the
implied crunching length is always eight characters.

The output is the krunched name. The output has an extension only if the
original argument was a file name with an extension.

@node Krunching Method,Examples of gnatkr Usage,Using gnatkr,File Name Krunching with gnatkr
@anchor{gnat_ugn/the_gnat_compilation_model id20}@anchor{68}@anchor{gnat_ugn/the_gnat_compilation_model krunching-method}@anchor{69}
@subsubsection Krunching Method


The initial file name is determined by the name of the unit that the file
contains. The name is formed by taking the full expanded name of the
unit and replacing the separating dots with hyphens and
using lowercase
for all letters, except that a hyphen in the second character position is
replaced by a tilde if the first character is
@code{a}, @code{i}, @code{g}, or @code{s}.
The extension is @code{.ads} for a
spec and @code{.adb} for a body.
Krunching does not affect the extension, but the file name is shortened to
the specified length by following these rules:


@itemize *

@item 
The name is divided into segments separated by hyphens, tildes or
underscores and all hyphens, tildes, and underscores are
eliminated. If this leaves the name short enough, we are done.

@item 
If the name is too long, the longest segment is located (left-most
if there are two of equal length), and shortened by dropping
its last character. This is repeated until the name is short enough.

As an example, consider the krunching of @code{our-strings-wide_fixed.adb}
to fit the name into 8 characters as required by some operating systems:

@example
our-strings-wide_fixed 22
our strings wide fixed 19
our string  wide fixed 18
our strin   wide fixed 17
our stri    wide fixed 16
our stri    wide fixe  15
our str     wide fixe  14
our str     wid  fixe  13
our str     wid  fix   12
ou  str     wid  fix   11
ou  st      wid  fix   10
ou  st      wi   fix   9
ou  st      wi   fi    8
Final file name: oustwifi.adb
@end example

@item 
The file names for all predefined units are always krunched to eight
characters. The krunching of these predefined units uses the following
special prefix replacements:


@multitable {xxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxx} 
@item

Prefix

@tab

Replacement

@item

@code{ada-}

@tab

@code{a-}

@item

@code{gnat-}

@tab

@code{g-}

@item

@code{interfac es-}

@tab

@code{i-}

@item

@code{system-}

@tab

@code{s-}

@end multitable


These system files have a hyphen in the second character position. That
is why normal user files replace such a character with a
tilde, to avoid confusion with system file names.

As an example of this special rule, consider
@code{ada-strings-wide_fixed.adb}, which gets krunched as follows:

@example
ada-strings-wide_fixed 22
a-  strings wide fixed 18
a-  string  wide fixed 17
a-  strin   wide fixed 16
a-  stri    wide fixed 15
a-  stri    wide fixe  14
a-  str     wide fixe  13
a-  str     wid  fixe  12
a-  str     wid  fix   11
a-  st      wid  fix   10
a-  st      wi   fix   9
a-  st      wi   fi    8
Final file name: a-stwifi.adb
@end example
@end itemize

Of course no file shortening algorithm can guarantee uniqueness over all
possible unit names, and if file name krunching is used then it is your
responsibility to ensure that no name clashes occur. The utility
program @code{gnatkr} is supplied for conveniently determining the
krunched name of a file.

@node Examples of gnatkr Usage,,Krunching Method,File Name Krunching with gnatkr
@anchor{gnat_ugn/the_gnat_compilation_model id21}@anchor{6a}@anchor{gnat_ugn/the_gnat_compilation_model examples-of-gnatkr-usage}@anchor{6b}
@subsubsection Examples of @code{gnatkr} Usage


@example
$ gnatkr very_long_unit_name.ads      --> velounna.ads
$ gnatkr grandparent-parent-child.ads --> grparchi.ads
$ gnatkr Grandparent.Parent.Child.ads --> grparchi.ads
$ gnatkr grandparent-parent-child     --> grparchi
$ gnatkr very_long_unit_name.ads/count=6 --> vlunna.ads
$ gnatkr very_long_unit_name.ads/count=0 --> very_long_unit_name.ads
@end example

@node Renaming Files with gnatchop,,File Name Krunching with gnatkr,File Naming Topics and Utilities
@anchor{gnat_ugn/the_gnat_compilation_model id22}@anchor{6c}@anchor{gnat_ugn/the_gnat_compilation_model renaming-files-with-gnatchop}@anchor{36}
@subsection Renaming Files with @code{gnatchop}


@geindex gnatchop

This section discusses how to handle files with multiple units by using
the @code{gnatchop} utility. This utility is also useful in renaming
files to meet the standard GNAT default file naming conventions.

@menu
* Handling Files with Multiple Units:: 
* Operating gnatchop in Compilation Mode:: 
* Command Line for gnatchop:: 
* Switches for gnatchop:: 
* Examples of gnatchop Usage:: 

@end menu

@node Handling Files with Multiple Units,Operating gnatchop in Compilation Mode,,Renaming Files with gnatchop
@anchor{gnat_ugn/the_gnat_compilation_model id23}@anchor{6d}@anchor{gnat_ugn/the_gnat_compilation_model handling-files-with-multiple-units}@anchor{6e}
@subsubsection Handling Files with Multiple Units


The basic compilation model of GNAT requires that a file submitted to the
compiler have only one unit and there be a strict correspondence
between the file name and the unit name.

The @code{gnatchop} utility allows both of these rules to be relaxed,
allowing GNAT to process files which contain multiple compilation units
and files with arbitrary file names. @code{gnatchop}
reads the specified file and generates one or more output files,
containing one unit per file. The unit and the file name correspond,
as required by GNAT.

If you want to permanently restructure a set of 'foreign' files so that
they match the GNAT rules, and do the remaining development using the
GNAT structure, you can simply use @code{gnatchop} once, generate the
new set of files and work with them from that point on.

Alternatively, if you want to keep your files in the 'foreign' format,
perhaps to maintain compatibility with some other Ada compilation
system, you can set up a procedure where you use @code{gnatchop} each
time you compile, regarding the source files that it writes as temporary
files that you throw away.

Note that if your file containing multiple units starts with a byte order
mark (BOM) specifying UTF-8 encoding, then the files generated by gnatchop
will each start with a copy of this BOM, meaning that they can be compiled
automatically in UTF-8 mode without needing to specify an explicit encoding.

@node Operating gnatchop in Compilation Mode,Command Line for gnatchop,Handling Files with Multiple Units,Renaming Files with gnatchop
@anchor{gnat_ugn/the_gnat_compilation_model operating-gnatchop-in-compilation-mode}@anchor{6f}@anchor{gnat_ugn/the_gnat_compilation_model id24}@anchor{70}
@subsubsection Operating gnatchop in Compilation Mode


The basic function of @code{gnatchop} is to take a file with multiple units
and split it into separate files. The boundary between files is reasonably
clear, except for the issue of comments and pragmas. In default mode, the
rule is that any pragmas between units belong to the previous unit, except
that configuration pragmas always belong to the following unit. Any comments
belong to the following unit. These rules
almost always result in the right choice of
the split point without needing to mark it explicitly and most users will
find this default to be what they want. In this default mode it is incorrect to
submit a file containing only configuration pragmas, or one that ends in
configuration pragmas, to @code{gnatchop}.

However, using a special option to activate 'compilation mode',
@code{gnatchop}
can perform another function, which is to provide exactly the semantics
required by the RM for handling of configuration pragmas in a compilation.
In the absence of configuration pragmas (at the main file level), this
option has no effect, but it causes such configuration pragmas to be handled
in a quite different manner.

First, in compilation mode, if @code{gnatchop} is given a file that consists of
only configuration pragmas, then this file is appended to the
@code{gnat.adc} file in the current directory. This behavior provides
the required behavior described in the RM for the actions to be taken
on submitting such a file to the compiler, namely that these pragmas
should apply to all subsequent compilations in the same compilation
environment. Using GNAT, the current directory, possibly containing a
@code{gnat.adc} file is the representation
of a compilation environment. For more information on the
@code{gnat.adc} file, see @ref{56,,Handling of Configuration Pragmas}.

Second, in compilation mode, if @code{gnatchop}
is given a file that starts with
configuration pragmas, and contains one or more units, then these
configuration pragmas are prepended to each of the chopped files. This
behavior provides the required behavior described in the RM for the
actions to be taken on compiling such a file, namely that the pragmas
apply to all units in the compilation, but not to subsequently compiled
units.

Finally, if configuration pragmas appear between units, they are appended
to the previous unit. This results in the previous unit being illegal,
since the compiler does not accept configuration pragmas that follow
a unit. This provides the required RM behavior that forbids configuration
pragmas other than those preceding the first compilation unit of a
compilation.

For most purposes, @code{gnatchop} will be used in default mode. The
compilation mode described above is used only if you need exactly
accurate behavior with respect to compilations, and you have files
that contain multiple units and configuration pragmas. In this
circumstance the use of @code{gnatchop} with the compilation mode
switch provides the required behavior, and is for example the mode
in which GNAT processes the ACVC tests.

@node Command Line for gnatchop,Switches for gnatchop,Operating gnatchop in Compilation Mode,Renaming Files with gnatchop
@anchor{gnat_ugn/the_gnat_compilation_model id25}@anchor{71}@anchor{gnat_ugn/the_gnat_compilation_model command-line-for-gnatchop}@anchor{72}
@subsubsection Command Line for @code{gnatchop}


The @code{gnatchop} command has the form:

@example
$ gnatchop switches file_name [file_name ...]
      [directory]
@end example

The only required argument is the file name of the file to be chopped.
There are no restrictions on the form of this file name. The file itself
contains one or more Ada units, in normal GNAT format, concatenated
together. As shown, more than one file may be presented to be chopped.

When run in default mode, @code{gnatchop} generates one output file in
the current directory for each unit in each of the files.

@code{directory}, if specified, gives the name of the directory to which
the output files will be written. If it is not specified, all files are
written to the current directory.

For example, given a
file called @code{hellofiles} containing

@example
procedure Hello;

with Ada.Text_IO; use Ada.Text_IO;
procedure Hello is
begin
   Put_Line ("Hello");
end Hello;
@end example

the command

@example
$ gnatchop hellofiles
@end example

generates two files in the current directory, one called
@code{hello.ads} containing the single line that is the procedure spec,
and the other called @code{hello.adb} containing the remaining text. The
original file is not affected. The generated files can be compiled in
the normal manner.

When gnatchop is invoked on a file that is empty or that contains only empty
lines and/or comments, gnatchop will not fail, but will not produce any
new sources.

For example, given a
file called @code{toto.txt} containing

@example
--  Just a comment
@end example

the command

@example
$ gnatchop toto.txt
@end example

will not produce any new file and will result in the following warnings:

@example
toto.txt:1:01: warning: empty file, contains no compilation units
no compilation units found
no source files written
@end example

@node Switches for gnatchop,Examples of gnatchop Usage,Command Line for gnatchop,Renaming Files with gnatchop
@anchor{gnat_ugn/the_gnat_compilation_model switches-for-gnatchop}@anchor{73}@anchor{gnat_ugn/the_gnat_compilation_model id26}@anchor{74}
@subsubsection Switches for @code{gnatchop}


@code{gnatchop} recognizes the following switches:

@geindex --version (gnatchop)


@table @asis

@item @code{--version}

Display Copyright and version, then exit disregarding all other options.
@end table

@geindex --help (gnatchop)


@table @asis

@item @code{--help}

If @code{--version} was not used, display usage, then exit disregarding
all other options.
@end table

@geindex -c (gnatchop)


@table @asis

@item @code{-c}

Causes @code{gnatchop} to operate in compilation mode, in which
configuration pragmas are handled according to strict RM rules. See
previous section for a full description of this mode.

@item @code{-gnat@emph{xxx}}

This passes the given @code{-gnat@emph{xxx}} switch to @code{gnat} which is
used to parse the given file. Not all @emph{xxx} options make sense,
but for example, the use of @code{-gnati2} allows @code{gnatchop} to
process a source file that uses Latin-2 coding for identifiers.

@item @code{-h}

Causes @code{gnatchop} to generate a brief help summary to the standard
output file showing usage information.
@end table

@geindex -k (gnatchop)


@table @asis

@item @code{-k@emph{mm}}

Limit generated file names to the specified number @code{mm}
of characters.
This is useful if the
resulting set of files is required to be interoperable with systems
which limit the length of file names.
No space is allowed between the @code{-k} and the numeric value. The numeric
value may be omitted in which case a default of @code{-k8},
suitable for use
with DOS-like file systems, is used. If no @code{-k} switch
is present then
there is no limit on the length of file names.
@end table

@geindex -p (gnatchop)


@table @asis

@item @code{-p}

Causes the file modification time stamp of the input file to be
preserved and used for the time stamp of the output file(s). This may be
useful for preserving coherency of time stamps in an environment where
@code{gnatchop} is used as part of a standard build process.
@end table

@geindex -q (gnatchop)


@table @asis

@item @code{-q}

Causes output of informational messages indicating the set of generated
files to be suppressed. Warnings and error messages are unaffected.
@end table

@geindex -r (gnatchop)

@geindex Source_Reference pragmas


@table @asis

@item @code{-r}

Generate @code{Source_Reference} pragmas. Use this switch if the output
files are regarded as temporary and development is to be done in terms
of the original unchopped file. This switch causes
@code{Source_Reference} pragmas to be inserted into each of the
generated files to refers back to the original file name and line number.
The result is that all error messages refer back to the original
unchopped file.
In addition, the debugging information placed into the object file (when
the @code{-g} switch of @code{gcc} or @code{gnatmake} is
specified)
also refers back to this original file so that tools like profilers and
debuggers will give information in terms of the original unchopped file.

If the original file to be chopped itself contains
a @code{Source_Reference}
pragma referencing a third file, then gnatchop respects
this pragma, and the generated @code{Source_Reference} pragmas
in the chopped file refer to the original file, with appropriate
line numbers. This is particularly useful when @code{gnatchop}
is used in conjunction with @code{gnatprep} to compile files that
contain preprocessing statements and multiple units.
@end table

@geindex -v (gnatchop)


@table @asis

@item @code{-v}

Causes @code{gnatchop} to operate in verbose mode. The version
number and copyright notice are output, as well as exact copies of
the gnat1 commands spawned to obtain the chop control information.
@end table

@geindex -w (gnatchop)


@table @asis

@item @code{-w}

Overwrite existing file names. Normally @code{gnatchop} regards it as a
fatal error if there is already a file with the same name as a
file it would otherwise output, in other words if the files to be
chopped contain duplicated units. This switch bypasses this
check, and causes all but the last instance of such duplicated
units to be skipped.
@end table

@geindex --GCC= (gnatchop)


@table @asis

@item @code{--GCC=@emph{xxxx}}

Specify the path of the GNAT parser to be used. When this switch is used,
no attempt is made to add the prefix to the GNAT parser executable.
@end table

@node Examples of gnatchop Usage,,Switches for gnatchop,Renaming Files with gnatchop
@anchor{gnat_ugn/the_gnat_compilation_model id27}@anchor{75}@anchor{gnat_ugn/the_gnat_compilation_model examples-of-gnatchop-usage}@anchor{76}
@subsubsection Examples of @code{gnatchop} Usage


@example
$ gnatchop -w hello_s.ada prerelease/files
@end example

Chops the source file @code{hello_s.ada}. The output files will be
placed in the directory @code{prerelease/files},
overwriting any
files with matching names in that directory (no files in the current
directory are modified).

@example
$ gnatchop archive
@end example

Chops the source file @code{archive}
into the current directory. One
useful application of @code{gnatchop} is in sending sets of sources
around, for example in email messages. The required sources are simply
concatenated (for example, using a Unix @code{cat}
command), and then
@code{gnatchop} is used at the other end to reconstitute the original
file names.

@example
$ gnatchop file1 file2 file3 direc
@end example

Chops all units in files @code{file1}, @code{file2}, @code{file3}, placing
the resulting files in the directory @code{direc}. Note that if any units
occur more than once anywhere within this set of files, an error message
is generated, and no files are written. To override this check, use the
@code{-w} switch,
in which case the last occurrence in the last file will
be the one that is output, and earlier duplicate occurrences for a given
unit will be skipped.

@node Configuration Pragmas,Generating Object Files,File Naming Topics and Utilities,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model id28}@anchor{77}@anchor{gnat_ugn/the_gnat_compilation_model configuration-pragmas}@anchor{14}
@section Configuration Pragmas


@geindex Configuration pragmas

@geindex Pragmas
@geindex configuration

Configuration pragmas include those pragmas described as
such in the Ada Reference Manual, as well as
implementation-dependent pragmas that are configuration pragmas.
See the @code{Implementation_Defined_Pragmas} chapter in the
@cite{GNAT_Reference_Manual} for details on these
additional GNAT-specific configuration pragmas.
Most notably, the pragma @code{Source_File_Name}, which allows
specifying non-default names for source files, is a configuration
pragma. The following is a complete list of configuration pragmas
recognized by GNAT:

@example
Ada_83
Ada_95
Ada_05
Ada_2005
Ada_12
Ada_2012
Allow_Integer_Address
Annotate
Assertion_Policy
Assume_No_Invalid_Values
C_Pass_By_Copy
Check_Float_Overflow
Check_Name
Check_Policy
Compile_Time_Error
Compile_Time_Warning
Compiler_Unit
Compiler_Unit_Warning
Component_Alignment
Convention_Identifier
Debug_Policy
Detect_Blocking
Default_Scalar_Storage_Order
Default_Storage_Pool
Disable_Atomic_Synchronization
Discard_Names
Elaboration_Checks
Eliminate
Enable_Atomic_Synchronization
Extend_System
Extensions_Allowed
External_Name_Casing
Fast_Math
Favor_Top_Level
Ignore_Pragma
Implicit_Packing
Initialize_Scalars
Interrupt_State
License
Locking_Policy
No_Component_Reordering
No_Heap_Finalization
No_Run_Time
No_Strict_Aliasing
Normalize_Scalars
Optimize_Alignment
Overflow_Mode
Overriding_Renamings
Partition_Elaboration_Policy
Persistent_BSS
Polling
Prefix_Exception_Messages
Priority_Specific_Dispatching
Profile
Profile_Warnings
Propagate_Exceptions
Queuing_Policy
Rational
Ravenscar
Rename_Pragma
Restricted_Run_Time
Restrictions
Restrictions_Warnings
Reviewable
Short_Circuit_And_Or
Short_Descriptors
Source_File_Name
Source_File_Name_Project
SPARK_Mode
Style_Checks
Suppress
Suppress_Exception_Locations
Task_Dispatching_Policy
Unevaluated_Use_Of_Old
Universal_Data
Unsuppress
Use_VADS_Size
Validity_Checks
Warning_As_Error
Warnings
Wide_Character_Encoding
@end example

@menu
* Handling of Configuration Pragmas:: 
* The Configuration Pragmas Files:: 

@end menu

@node Handling of Configuration Pragmas,The Configuration Pragmas Files,,Configuration Pragmas
@anchor{gnat_ugn/the_gnat_compilation_model id29}@anchor{78}@anchor{gnat_ugn/the_gnat_compilation_model handling-of-configuration-pragmas}@anchor{56}
@subsection Handling of Configuration Pragmas


Configuration pragmas may either appear at the start of a compilation
unit, or they can appear in a configuration pragma file to apply to
all compilations performed in a given compilation environment.

GNAT also provides the @code{gnatchop} utility to provide an automatic
way to handle configuration pragmas following the semantics for
compilations (that is, files with multiple units), described in the RM.
See @ref{6f,,Operating gnatchop in Compilation Mode} for details.
However, for most purposes, it will be more convenient to edit the
@code{gnat.adc} file that contains configuration pragmas directly,
as described in the following section.

In the case of @code{Restrictions} pragmas appearing as configuration
pragmas in individual compilation units, the exact handling depends on
the type of restriction.

Restrictions that require partition-wide consistency (like
@code{No_Tasking}) are
recognized wherever they appear
and can be freely inherited, e.g. from a @emph{with}ed unit to the @emph{with}ing
unit. This makes sense since the binder will in any case insist on seeing
consistent use, so any unit not conforming to any restrictions that are
anywhere in the partition will be rejected, and you might as well find
that out at compile time rather than at bind time.

For restrictions that do not require partition-wide consistency, e.g.
SPARK or No_Implementation_Attributes, in general the restriction applies
only to the unit in which the pragma appears, and not to any other units.

The exception is No_Elaboration_Code which always applies to the entire
object file from a compilation, i.e. to the body, spec, and all subunits.
This restriction can be specified in a configuration pragma file, or it
can be on the body and/or the spec (in eithe case it applies to all the
relevant units). It can appear on a subunit only if it has previously
appeared in the body of spec.

@node The Configuration Pragmas Files,,Handling of Configuration Pragmas,Configuration Pragmas
@anchor{gnat_ugn/the_gnat_compilation_model the-configuration-pragmas-files}@anchor{79}@anchor{gnat_ugn/the_gnat_compilation_model id30}@anchor{7a}
@subsection The Configuration Pragmas Files


@geindex gnat.adc

In GNAT a compilation environment is defined by the current
directory at the time that a compile command is given. This current
directory is searched for a file whose name is @code{gnat.adc}. If
this file is present, it is expected to contain one or more
configuration pragmas that will be applied to the current compilation.
However, if the switch @code{-gnatA} is used, @code{gnat.adc} is not
considered. When taken into account, @code{gnat.adc} is added to the
dependencies, so that if @code{gnat.adc} is modified later, an invocation of
@code{gnatmake} will recompile the source.

Configuration pragmas may be entered into the @code{gnat.adc} file
either by running @code{gnatchop} on a source file that consists only of
configuration pragmas, or more conveniently by direct editing of the
@code{gnat.adc} file, which is a standard format source file.

Besides @code{gnat.adc}, additional files containing configuration
pragmas may be applied to the current compilation using the switch
@code{-gnatec=@emph{path}} where @code{path} must designate an existing file that
contains only configuration pragmas. These configuration pragmas are
in addition to those found in @code{gnat.adc} (provided @code{gnat.adc}
is present and switch @code{-gnatA} is not used).

It is allowable to specify several switches @code{-gnatec=}, all of which
will be taken into account.

Files containing configuration pragmas specified with switches
@code{-gnatec=} are added to the dependencies, unless they are
temporary files. A file is considered temporary if its name ends in
@code{.tmp} or @code{.TMP}. Certain tools follow this naming
convention because they pass information to @code{gcc} via
temporary files that are immediately deleted; it doesn't make sense to
depend on a file that no longer exists. Such tools include
@code{gprbuild}, @code{gnatmake}, and @code{gnatcheck}.

If you are using project file, a separate mechanism is provided using
project attributes.

@c --Comment
@c See :ref:`Specifying_Configuration_Pragmas` for more details.

@node Generating Object Files,Source Dependencies,Configuration Pragmas,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model generating-object-files}@anchor{40}@anchor{gnat_ugn/the_gnat_compilation_model id31}@anchor{7b}
@section Generating Object Files


An Ada program consists of a set of source files, and the first step in
compiling the program is to generate the corresponding object files.
These are generated by compiling a subset of these source files.
The files you need to compile are the following:


@itemize *

@item 
If a package spec has no body, compile the package spec to produce the
object file for the package.

@item 
If a package has both a spec and a body, compile the body to produce the
object file for the package. The source file for the package spec need
not be compiled in this case because there is only one object file, which
contains the code for both the spec and body of the package.

@item 
For a subprogram, compile the subprogram body to produce the object file
for the subprogram. The spec, if one is present, is as usual in a
separate file, and need not be compiled.
@end itemize

@geindex Subunits


@itemize *

@item 
In the case of subunits, only compile the parent unit. A single object
file is generated for the entire subunit tree, which includes all the
subunits.

@item 
Compile child units independently of their parent units
(though, of course, the spec of all the ancestor unit must be present in order
to compile a child unit).

@geindex Generics

@item 
Compile generic units in the same manner as any other units. The object
files in this case are small dummy files that contain at most the
flag used for elaboration checking. This is because GNAT always handles generic
instantiation by means of macro expansion. However, it is still necessary to
compile generic units, for dependency checking and elaboration purposes.
@end itemize

The preceding rules describe the set of files that must be compiled to
generate the object files for a program. Each object file has the same
name as the corresponding source file, except that the extension is
@code{.o} as usual.

You may wish to compile other files for the purpose of checking their
syntactic and semantic correctness. For example, in the case where a
package has a separate spec and body, you would not normally compile the
spec. However, it is convenient in practice to compile the spec to make
sure it is error-free before compiling clients of this spec, because such
compilations will fail if there is an error in the spec.

GNAT provides an option for compiling such files purely for the
purposes of checking correctness; such compilations are not required as
part of the process of building a program. To compile a file in this
checking mode, use the @code{-gnatc} switch.

@node Source Dependencies,The Ada Library Information Files,Generating Object Files,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model id32}@anchor{7c}@anchor{gnat_ugn/the_gnat_compilation_model source-dependencies}@anchor{41}
@section Source Dependencies


A given object file clearly depends on the source file which is compiled
to produce it. Here we are using "depends" in the sense of a typical
@code{make} utility; in other words, an object file depends on a source
file if changes to the source file require the object file to be
recompiled.
In addition to this basic dependency, a given object may depend on
additional source files as follows:


@itemize *

@item 
If a file being compiled @emph{with}s a unit @code{X}, the object file
depends on the file containing the spec of unit @code{X}. This includes
files that are @emph{with}ed implicitly either because they are parents
of @emph{with}ed child units or they are run-time units required by the
language constructs used in a particular unit.

@item 
If a file being compiled instantiates a library level generic unit, the
object file depends on both the spec and body files for this generic
unit.

@item 
If a file being compiled instantiates a generic unit defined within a
package, the object file depends on the body file for the package as
well as the spec file.
@end itemize

@geindex Inline

@geindex -gnatn switch


@itemize *

@item 
If a file being compiled contains a call to a subprogram for which
pragma @code{Inline} applies and inlining is activated with the
@code{-gnatn} switch, the object file depends on the file containing the
body of this subprogram as well as on the file containing the spec. Note
that for inlining to actually occur as a result of the use of this switch,
it is necessary to compile in optimizing mode.

@geindex -gnatN switch

The use of @code{-gnatN} activates  inlining optimization
that is performed by the front end of the compiler. This inlining does
not require that the code generation be optimized. Like @code{-gnatn},
the use of this switch generates additional dependencies.

When using a gcc-based back end (in practice this means using any version
of GNAT other than for the JVM, .NET or GNAAMP platforms), then the use of
@code{-gnatN} is deprecated, and the use of @code{-gnatn} is preferred.
Historically front end inlining was more extensive than the gcc back end
inlining, but that is no longer the case.

@item 
If an object file @code{O} depends on the proper body of a subunit through
inlining or instantiation, it depends on the parent unit of the subunit.
This means that any modification of the parent unit or one of its subunits
affects the compilation of @code{O}.

@item 
The object file for a parent unit depends on all its subunit body files.

@item 
The previous two rules meant that for purposes of computing dependencies and
recompilation, a body and all its subunits are treated as an indivisible whole.

These rules are applied transitively: if unit @code{A} @emph{with}s
unit @code{B}, whose elaboration calls an inlined procedure in package
@code{C}, the object file for unit @code{A} will depend on the body of
@code{C}, in file @code{c.adb}.

The set of dependent files described by these rules includes all the
files on which the unit is semantically dependent, as dictated by the
Ada language standard. However, it is a superset of what the
standard describes, because it includes generic, inline, and subunit
dependencies.

An object file must be recreated by recompiling the corresponding source
file if any of the source files on which it depends are modified. For
example, if the @code{make} utility is used to control compilation,
the rule for an Ada object file must mention all the source files on
which the object file depends, according to the above definition.
The determination of the necessary
recompilations is done automatically when one uses @code{gnatmake}.
@end itemize

@node The Ada Library Information Files,Binding an Ada Program,Source Dependencies,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model id33}@anchor{7d}@anchor{gnat_ugn/the_gnat_compilation_model the-ada-library-information-files}@anchor{42}
@section The Ada Library Information Files


@geindex Ada Library Information files

@geindex ALI files

Each compilation actually generates two output files. The first of these
is the normal object file that has a @code{.o} extension. The second is a
text file containing full dependency information. It has the same
name as the source file, but an @code{.ali} extension.
This file is known as the Ada Library Information (@code{ALI}) file.
The following information is contained in the @code{ALI} file.


@itemize *

@item 
Version information (indicates which version of GNAT was used to compile
the unit(s) in question)

@item 
Main program information (including priority and time slice settings,
as well as the wide character encoding used during compilation).

@item 
List of arguments used in the @code{gcc} command for the compilation

@item 
Attributes of the unit, including configuration pragmas used, an indication
of whether the compilation was successful, exception model used etc.

@item 
A list of relevant restrictions applying to the unit (used for consistency)
checking.

@item 
Categorization information (e.g., use of pragma @code{Pure}).

@item 
Information on all @emph{with}ed units, including presence of
@code{Elaborate} or @code{Elaborate_All} pragmas.

@item 
Information from any @code{Linker_Options} pragmas used in the unit

@item 
Information on the use of @code{Body_Version} or @code{Version}
attributes in the unit.

@item 
Dependency information. This is a list of files, together with
time stamp and checksum information. These are files on which
the unit depends in the sense that recompilation is required
if any of these units are modified.

@item 
Cross-reference data. Contains information on all entities referenced
in the unit. Used by tools like @code{gnatxref} and @code{gnatfind} to
provide cross-reference information.
@end itemize

For a full detailed description of the format of the @code{ALI} file,
see the source of the body of unit @code{Lib.Writ}, contained in file
@code{lib-writ.adb} in the GNAT compiler sources.

@node Binding an Ada Program,GNAT and Libraries,The Ada Library Information Files,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model id34}@anchor{7e}@anchor{gnat_ugn/the_gnat_compilation_model binding-an-ada-program}@anchor{43}
@section Binding an Ada Program


When using languages such as C and C++, once the source files have been
compiled the only remaining step in building an executable program
is linking the object modules together. This means that it is possible to
link an inconsistent version of a program, in which two units have
included different versions of the same header.

The rules of Ada do not permit such an inconsistent program to be built.
For example, if two clients have different versions of the same package,
it is illegal to build a program containing these two clients.
These rules are enforced by the GNAT binder, which also determines an
elaboration order consistent with the Ada rules.

The GNAT binder is run after all the object files for a program have
been created. It is given the name of the main program unit, and from
this it determines the set of units required by the program, by reading the
corresponding ALI files. It generates error messages if the program is
inconsistent or if no valid order of elaboration exists.

If no errors are detected, the binder produces a main program, in Ada by
default, that contains calls to the elaboration procedures of those
compilation unit that require them, followed by
a call to the main program. This Ada program is compiled to generate the
object file for the main program. The name of
the Ada file is @code{b~xxx}.adb` (with the corresponding spec
@code{b~xxx}.ads`) where @code{xxx} is the name of the
main program unit.

Finally, the linker is used to build the resulting executable program,
using the object from the main program from the bind step as well as the
object files for the Ada units of the program.

@node GNAT and Libraries,Conditional Compilation,Binding an Ada Program,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model gnat-and-libraries}@anchor{15}@anchor{gnat_ugn/the_gnat_compilation_model id35}@anchor{7f}
@section GNAT and Libraries


@geindex Library building and using

This section describes how to build and use libraries with GNAT, and also shows
how to recompile the GNAT run-time library. You should be familiar with the
Project Manager facility (see the @emph{GNAT_Project_Manager} chapter of the
@emph{GPRbuild User's Guide}) before reading this chapter.

@menu
* Introduction to Libraries in GNAT:: 
* General Ada Libraries:: 
* Stand-alone Ada Libraries:: 
* Rebuilding the GNAT Run-Time Library:: 

@end menu

@node Introduction to Libraries in GNAT,General Ada Libraries,,GNAT and Libraries
@anchor{gnat_ugn/the_gnat_compilation_model introduction-to-libraries-in-gnat}@anchor{80}@anchor{gnat_ugn/the_gnat_compilation_model id36}@anchor{81}
@subsection Introduction to Libraries in GNAT


A library is, conceptually, a collection of objects which does not have its
own main thread of execution, but rather provides certain services to the
applications that use it. A library can be either statically linked with the
application, in which case its code is directly included in the application,
or, on platforms that support it, be dynamically linked, in which case
its code is shared by all applications making use of this library.

GNAT supports both types of libraries.
In the static case, the compiled code can be provided in different ways. The
simplest approach is to provide directly the set of objects resulting from
compilation of the library source files. Alternatively, you can group the
objects into an archive using whatever commands are provided by the operating
system. For the latter case, the objects are grouped into a shared library.

In the GNAT environment, a library has three types of components:


@itemize *

@item 
Source files,

@item 
@code{ALI} files (see @ref{42,,The Ada Library Information Files}), and

@item 
Object files, an archive or a shared library.
@end itemize

A GNAT library may expose all its source files, which is useful for
documentation purposes. Alternatively, it may expose only the units needed by
an external user to make use of the library. That is to say, the specs
reflecting the library services along with all the units needed to compile
those specs, which can include generic bodies or any body implementing an
inlined routine. In the case of @emph{stand-alone libraries} those exposed
units are called @emph{interface units} (@ref{82,,Stand-alone Ada Libraries}).

All compilation units comprising an application, including those in a library,
need to be elaborated in an order partially defined by Ada's semantics. GNAT
computes the elaboration order from the @code{ALI} files and this is why they
constitute a mandatory part of GNAT libraries.
@emph{Stand-alone libraries} are the exception to this rule because a specific
library elaboration routine is produced independently of the application(s)
using the library.

@node General Ada Libraries,Stand-alone Ada Libraries,Introduction to Libraries in GNAT,GNAT and Libraries
@anchor{gnat_ugn/the_gnat_compilation_model general-ada-libraries}@anchor{83}@anchor{gnat_ugn/the_gnat_compilation_model id37}@anchor{84}
@subsection General Ada Libraries


@menu
* Building a library:: 
* Installing a library:: 
* Using a library:: 

@end menu

@node Building a library,Installing a library,,General Ada Libraries
@anchor{gnat_ugn/the_gnat_compilation_model building-a-library}@anchor{85}@anchor{gnat_ugn/the_gnat_compilation_model id38}@anchor{86}
@subsubsection Building a library


The easiest way to build a library is to use the Project Manager,
which supports a special type of project called a @emph{Library Project}
(see the @emph{Library Projects} section in the @emph{GNAT Project Manager}
chapter of the @emph{GPRbuild User's Guide}).

A project is considered a library project, when two project-level attributes
are defined in it: @code{Library_Name} and @code{Library_Dir}. In order to
control different aspects of library configuration, additional optional
project-level attributes can be specified:


@itemize *

@item 

@table @asis

@item @code{Library_Kind}

This attribute controls whether the library is to be static or dynamic
@end table

@item 

@table @asis

@item @code{Library_Version}

This attribute specifies the library version; this value is used
during dynamic linking of shared libraries to determine if the currently
installed versions of the binaries are compatible.
@end table

@item 
@code{Library_Options}

@item 

@table @asis

@item @code{Library_GCC}

These attributes specify additional low-level options to be used during
library generation, and redefine the actual application used to generate
library.
@end table
@end itemize

The GNAT Project Manager takes full care of the library maintenance task,
including recompilation of the source files for which objects do not exist
or are not up to date, assembly of the library archive, and installation of
the library (i.e., copying associated source, object and @code{ALI} files
to the specified location).

Here is a simple library project file:

@example
project My_Lib is
  for Source_Dirs use ("src1", "src2");
  for Object_Dir use "obj";
  for Library_Name use "mylib";
  for Library_Dir use "lib";
  for Library_Kind use "dynamic";
end My_lib;
@end example

and the compilation command to build and install the library:

@example
$ gnatmake -Pmy_lib
@end example

It is not entirely trivial to perform manually all the steps required to
produce a library. We recommend that you use the GNAT Project Manager
for this task. In special cases where this is not desired, the necessary
steps are discussed below.

There are various possibilities for compiling the units that make up the
library: for example with a Makefile (@ref{1f,,Using the GNU make Utility}) or
with a conventional script. For simple libraries, it is also possible to create
a dummy main program which depends upon all the packages that comprise the
interface of the library. This dummy main program can then be given to
@code{gnatmake}, which will ensure that all necessary objects are built.

After this task is accomplished, you should follow the standard procedure
of the underlying operating system to produce the static or shared library.

Here is an example of such a dummy program:

@example
with My_Lib.Service1;
with My_Lib.Service2;
with My_Lib.Service3;
procedure My_Lib_Dummy is
begin
   null;
end;
@end example

Here are the generic commands that will build an archive or a shared library.

@example
# compiling the library
$ gnatmake -c my_lib_dummy.adb

# we don't need the dummy object itself
$ rm my_lib_dummy.o my_lib_dummy.ali

# create an archive with the remaining objects
$ ar rc libmy_lib.a *.o
# some systems may require "ranlib" to be run as well

# or create a shared library
$ gcc -shared -o libmy_lib.so *.o
# some systems may require the code to have been compiled with -fPIC

# remove the object files that are now in the library
$ rm *.o

# Make the ALI files read-only so that gnatmake will not try to
# regenerate the objects that are in the library
$ chmod -w *.ali
@end example

Please note that the library must have a name of the form @code{lib@emph{xxx}.a}
or @code{lib@emph{xxx}.so} (or @code{lib@emph{xxx}.dll} on Windows) in order to
be accessed by the directive @code{-l@emph{xxx}} at link time.

@node Installing a library,Using a library,Building a library,General Ada Libraries
@anchor{gnat_ugn/the_gnat_compilation_model installing-a-library}@anchor{87}@anchor{gnat_ugn/the_gnat_compilation_model id39}@anchor{88}
@subsubsection Installing a library


@geindex ADA_PROJECT_PATH

@geindex GPR_PROJECT_PATH

If you use project files, library installation is part of the library build
process (see the @emph{Installing a Library with Project Files} section of the
@emph{GNAT Project Manager} chapter of the @emph{GPRbuild User's Guide}).

When project files are not an option, it is also possible, but not recommended,
to install the library so that the sources needed to use the library are on the
Ada source path and the ALI files & libraries be on the Ada Object path (see
@ref{89,,Search Paths and the Run-Time Library (RTL)}. Alternatively, the system
administrator can place general-purpose libraries in the default compiler
paths, by specifying the libraries' location in the configuration files
@code{ada_source_path} and @code{ada_object_path}. These configuration files
must be located in the GNAT installation tree at the same place as the gcc spec
file. The location of the gcc spec file can be determined as follows:

@example
$ gcc -v
@end example

The configuration files mentioned above have a simple format: each line
must contain one unique directory name.
Those names are added to the corresponding path
in their order of appearance in the file. The names can be either absolute
or relative; in the latter case, they are relative to where theses files
are located.

The files @code{ada_source_path} and @code{ada_object_path} might not be
present in a
GNAT installation, in which case, GNAT will look for its run-time library in
the directories @code{adainclude} (for the sources) and @code{adalib} (for the
objects and @code{ALI} files). When the files exist, the compiler does not
look in @code{adainclude} and @code{adalib}, and thus the
@code{ada_source_path} file
must contain the location for the GNAT run-time sources (which can simply
be @code{adainclude}). In the same way, the @code{ada_object_path} file must
contain the location for the GNAT run-time objects (which can simply
be @code{adalib}).

You can also specify a new default path to the run-time library at compilation
time with the switch @code{--RTS=rts-path}. You can thus choose / change
the run-time library you want your program to be compiled with. This switch is
recognized by @code{gcc}, @code{gnatmake}, @code{gnatbind},
@code{gnatls}, @code{gnatfind} and @code{gnatxref}.

It is possible to install a library before or after the standard GNAT
library, by reordering the lines in the configuration files. In general, a
library must be installed before the GNAT library if it redefines
any part of it.

@node Using a library,,Installing a library,General Ada Libraries
@anchor{gnat_ugn/the_gnat_compilation_model using-a-library}@anchor{8a}@anchor{gnat_ugn/the_gnat_compilation_model id40}@anchor{8b}
@subsubsection Using a library


Once again, the project facility greatly simplifies the use of
libraries. In this context, using a library is just a matter of adding a
@emph{with} clause in the user project. For instance, to make use of the
library @code{My_Lib} shown in examples in earlier sections, you can
write:

@example
with "my_lib";
project My_Proj is
  ...
end My_Proj;
@end example

Even if you have a third-party, non-Ada library, you can still use GNAT's
Project Manager facility to provide a wrapper for it. For example, the
following project, when @emph{with}ed by your main project, will link with the
third-party library @code{liba.a}:

@example
project Liba is
   for Externally_Built use "true";
   for Source_Files use ();
   for Library_Dir use "lib";
   for Library_Name use "a";
   for Library_Kind use "static";
end Liba;
@end example

This is an alternative to the use of @code{pragma Linker_Options}. It is
especially interesting in the context of systems with several interdependent
static libraries where finding a proper linker order is not easy and best be
left to the tools having visibility over project dependence information.

In order to use an Ada library manually, you need to make sure that this
library is on both your source and object path
(see @ref{89,,Search Paths and the Run-Time Library (RTL)}
and @ref{8c,,Search Paths for gnatbind}). Furthermore, when the objects are grouped
in an archive or a shared library, you need to specify the desired
library at link time.

For example, you can use the library @code{mylib} installed in
@code{/dir/my_lib_src} and @code{/dir/my_lib_obj} with the following commands:

@example
$ gnatmake -aI/dir/my_lib_src -aO/dir/my_lib_obj my_appl \\
  -largs -lmy_lib
@end example

This can be expressed more simply:

@example
$ gnatmake my_appl
@end example

when the following conditions are met:


@itemize *

@item 
@code{/dir/my_lib_src} has been added by the user to the environment
variable 
@geindex ADA_INCLUDE_PATH
@geindex environment variable; ADA_INCLUDE_PATH
@code{ADA_INCLUDE_PATH}, or by the administrator to the file
@code{ada_source_path}

@item 
@code{/dir/my_lib_obj} has been added by the user to the environment
variable 
@geindex ADA_OBJECTS_PATH
@geindex environment variable; ADA_OBJECTS_PATH
@code{ADA_OBJECTS_PATH}, or by the administrator to the file
@code{ada_object_path}

@item 
a pragma @code{Linker_Options} has been added to one of the sources.
For example:

@example
pragma Linker_Options ("-lmy_lib");
@end example
@end itemize

Note that you may also load a library dynamically at
run time given its filename, as illustrated in the GNAT @code{plugins} example
in the directory @code{share/examples/gnat/plugins} within the GNAT
install area.

@node Stand-alone Ada Libraries,Rebuilding the GNAT Run-Time Library,General Ada Libraries,GNAT and Libraries
@anchor{gnat_ugn/the_gnat_compilation_model stand-alone-ada-libraries}@anchor{82}@anchor{gnat_ugn/the_gnat_compilation_model id41}@anchor{8d}
@subsection Stand-alone Ada Libraries


@geindex Stand-alone libraries

@menu
* Introduction to Stand-alone Libraries:: 
* Building a Stand-alone Library:: 
* Creating a Stand-alone Library to be used in a non-Ada context:: 
* Restrictions in Stand-alone Libraries:: 

@end menu

@node Introduction to Stand-alone Libraries,Building a Stand-alone Library,,Stand-alone Ada Libraries
@anchor{gnat_ugn/the_gnat_compilation_model introduction-to-stand-alone-libraries}@anchor{8e}@anchor{gnat_ugn/the_gnat_compilation_model id42}@anchor{8f}
@subsubsection Introduction to Stand-alone Libraries


A Stand-alone Library (abbreviated 'SAL') is a library that contains the
necessary code to
elaborate the Ada units that are included in the library. In contrast with
an ordinary library, which consists of all sources, objects and @code{ALI}
files of the
library, a SAL may specify a restricted subset of compilation units
to serve as a library interface. In this case, the fully
self-sufficient set of files will normally consist of an objects
archive, the sources of interface units' specs, and the @code{ALI}
files of interface units.
If an interface spec contains a generic unit or an inlined subprogram,
the body's
source must also be provided; if the units that must be provided in the source
form depend on other units, the source and @code{ALI} files of those must
also be provided.

The main purpose of a SAL is to minimize the recompilation overhead of client
applications when a new version of the library is installed. Specifically,
if the interface sources have not changed, client applications do not need to
be recompiled. If, furthermore, a SAL is provided in the shared form and its
version, controlled by @code{Library_Version} attribute, is not changed,
then the clients do not need to be relinked.

SALs also allow the library providers to minimize the amount of library source
text exposed to the clients.  Such 'information hiding' might be useful or
necessary for various reasons.

Stand-alone libraries are also well suited to be used in an executable whose
main routine is not written in Ada.

@node Building a Stand-alone Library,Creating a Stand-alone Library to be used in a non-Ada context,Introduction to Stand-alone Libraries,Stand-alone Ada Libraries
@anchor{gnat_ugn/the_gnat_compilation_model id43}@anchor{90}@anchor{gnat_ugn/the_gnat_compilation_model building-a-stand-alone-library}@anchor{91}
@subsubsection Building a Stand-alone Library


GNAT's Project facility provides a simple way of building and installing
stand-alone libraries; see the @emph{Stand-alone Library Projects} section
in the @emph{GNAT Project Manager} chapter of the @emph{GPRbuild User's Guide}.
To be a Stand-alone Library Project, in addition to the two attributes
that make a project a Library Project (@code{Library_Name} and
@code{Library_Dir}; see the @emph{Library Projects} section in the
@emph{GNAT Project Manager} chapter of the @emph{GPRbuild User's Guide}),
the attribute @code{Library_Interface} must be defined.  For example:

@example
for Library_Dir use "lib_dir";
for Library_Name use "dummy";
for Library_Interface use ("int1", "int1.child");
@end example

Attribute @code{Library_Interface} has a non-empty string list value,
each string in the list designating a unit contained in an immediate source
of the project file.

When a Stand-alone Library is built, first the binder is invoked to build
a package whose name depends on the library name
(@code{b~dummy.ads/b} in the example above).
This binder-generated package includes initialization and
finalization procedures whose
names depend on the library name (@code{dummyinit} and @code{dummyfinal}
in the example
above). The object corresponding to this package is included in the library.

You must ensure timely (e.g., prior to any use of interfaces in the SAL)
calling of these procedures if a static SAL is built, or if a shared SAL
is built
with the project-level attribute @code{Library_Auto_Init} set to
@code{"false"}.

For a Stand-Alone Library, only the @code{ALI} files of the Interface Units
(those that are listed in attribute @code{Library_Interface}) are copied to
the Library Directory. As a consequence, only the Interface Units may be
imported from Ada units outside of the library. If other units are imported,
the binding phase will fail.

It is also possible to build an encapsulated library where not only
the code to elaborate and finalize the library is embedded but also
ensuring that the library is linked only against static
libraries. So an encapsulated library only depends on system
libraries, all other code, including the GNAT runtime, is embedded. To
build an encapsulated library the attribute
@code{Library_Standalone} must be set to @code{encapsulated}:

@example
for Library_Dir use "lib_dir";
for Library_Name use "dummy";
for Library_Kind use "dynamic";
for Library_Interface use ("int1", "int1.child");
for Library_Standalone use "encapsulated";
@end example

The default value for this attribute is @code{standard} in which case
a stand-alone library is built.

The attribute @code{Library_Src_Dir} may be specified for a
Stand-Alone Library. @code{Library_Src_Dir} is a simple attribute that has a
single string value. Its value must be the path (absolute or relative to the
project directory) of an existing directory. This directory cannot be the
object directory or one of the source directories, but it can be the same as
the library directory. The sources of the Interface
Units of the library that are needed by an Ada client of the library will be
copied to the designated directory, called the Interface Copy directory.
These sources include the specs of the Interface Units, but they may also
include bodies and subunits, when pragmas @code{Inline} or @code{Inline_Always}
are used, or when there is a generic unit in the spec. Before the sources
are copied to the Interface Copy directory, an attempt is made to delete all
files in the Interface Copy directory.

Building stand-alone libraries by hand is somewhat tedious, but for those
occasions when it is necessary here are the steps that you need to perform:


@itemize *

@item 
Compile all library sources.

@item 
Invoke the binder with the switch @code{-n} (No Ada main program),
with all the @code{ALI} files of the interfaces, and
with the switch @code{-L} to give specific names to the @code{init}
and @code{final} procedures.  For example:

@example
$ gnatbind -n int1.ali int2.ali -Lsal1
@end example

@item 
Compile the binder generated file:

@example
$ gcc -c b~int2.adb
@end example

@item 
Link the dynamic library with all the necessary object files,
indicating to the linker the names of the @code{init} (and possibly
@code{final}) procedures for automatic initialization (and finalization).
The built library should be placed in a directory different from
the object directory.

@item 
Copy the @code{ALI} files of the interface to the library directory,
add in this copy an indication that it is an interface to a SAL
(i.e., add a word @code{SL} on the line in the @code{ALI} file that starts
with letter 'P') and make the modified copy of the @code{ALI} file
read-only.
@end itemize

Using SALs is not different from using other libraries
(see @ref{8a,,Using a library}).

@node Creating a Stand-alone Library to be used in a non-Ada context,Restrictions in Stand-alone Libraries,Building a Stand-alone Library,Stand-alone Ada Libraries
@anchor{gnat_ugn/the_gnat_compilation_model creating-a-stand-alone-library-to-be-used-in-a-non-ada-context}@anchor{92}@anchor{gnat_ugn/the_gnat_compilation_model id44}@anchor{93}
@subsubsection Creating a Stand-alone Library to be used in a non-Ada context


It is easy to adapt the SAL build procedure discussed above for use of a SAL in
a non-Ada context.

The only extra step required is to ensure that library interface subprograms
are compatible with the main program, by means of @code{pragma Export}
or @code{pragma Convention}.

Here is an example of simple library interface for use with C main program:

@example
package My_Package is

   procedure Do_Something;
   pragma Export (C, Do_Something, "do_something");

   procedure Do_Something_Else;
   pragma Export (C, Do_Something_Else, "do_something_else");

end My_Package;
@end example

On the foreign language side, you must provide a 'foreign' view of the
library interface; remember that it should contain elaboration routines in
addition to interface subprograms.

The example below shows the content of @code{mylib_interface.h} (note
that there is no rule for the naming of this file, any name can be used)

@example
/* the library elaboration procedure */
extern void mylibinit (void);

/* the library finalization procedure */
extern void mylibfinal (void);

/* the interface exported by the library */
extern void do_something (void);
extern void do_something_else (void);
@end example

Libraries built as explained above can be used from any program, provided
that the elaboration procedures (named @code{mylibinit} in the previous
example) are called before the library services are used. Any number of
libraries can be used simultaneously, as long as the elaboration
procedure of each library is called.

Below is an example of a C program that uses the @code{mylib} library.

@example
#include "mylib_interface.h"

int
main (void)
@{
   /* First, elaborate the library before using it */
   mylibinit ();

   /* Main program, using the library exported entities */
   do_something ();
   do_something_else ();

   /* Library finalization at the end of the program */
   mylibfinal ();
   return 0;
@}
@end example

Note that invoking any library finalization procedure generated by
@code{gnatbind} shuts down the Ada run-time environment.
Consequently, the
finalization of all Ada libraries must be performed at the end of the program.
No call to these libraries or to the Ada run-time library should be made
after the finalization phase.

Note also that special care must be taken with multi-tasks
applications. The initialization and finalization routines are not
protected against concurrent access. If such requirement is needed it
must be ensured at the application level using a specific operating
system services like a mutex or a critical-section.

@node Restrictions in Stand-alone Libraries,,Creating a Stand-alone Library to be used in a non-Ada context,Stand-alone Ada Libraries
@anchor{gnat_ugn/the_gnat_compilation_model id45}@anchor{94}@anchor{gnat_ugn/the_gnat_compilation_model restrictions-in-stand-alone-libraries}@anchor{95}
@subsubsection Restrictions in Stand-alone Libraries


The pragmas listed below should be used with caution inside libraries,
as they can create incompatibilities with other Ada libraries:


@itemize *

@item 
pragma @code{Locking_Policy}

@item 
pragma @code{Partition_Elaboration_Policy}

@item 
pragma @code{Queuing_Policy}

@item 
pragma @code{Task_Dispatching_Policy}

@item 
pragma @code{Unreserve_All_Interrupts}
@end itemize

When using a library that contains such pragmas, the user must make sure
that all libraries use the same pragmas with the same values. Otherwise,
@code{Program_Error} will
be raised during the elaboration of the conflicting
libraries. The usage of these pragmas and its consequences for the user
should therefore be well documented.

Similarly, the traceback in the exception occurrence mechanism should be
enabled or disabled in a consistent manner across all libraries.
Otherwise, Program_Error will be raised during the elaboration of the
conflicting libraries.

If the @code{Version} or @code{Body_Version}
attributes are used inside a library, then you need to
perform a @code{gnatbind} step that specifies all @code{ALI} files in all
libraries, so that version identifiers can be properly computed.
In practice these attributes are rarely used, so this is unlikely
to be a consideration.

@node Rebuilding the GNAT Run-Time Library,,Stand-alone Ada Libraries,GNAT and Libraries
@anchor{gnat_ugn/the_gnat_compilation_model id46}@anchor{96}@anchor{gnat_ugn/the_gnat_compilation_model rebuilding-the-gnat-run-time-library}@anchor{97}
@subsection Rebuilding the GNAT Run-Time Library


@geindex GNAT Run-Time Library
@geindex rebuilding

@geindex Building the GNAT Run-Time Library

@geindex Rebuilding the GNAT Run-Time Library

@geindex Run-Time Library
@geindex rebuilding

It may be useful to recompile the GNAT library in various contexts, the
most important one being the use of partition-wide configuration pragmas
such as @code{Normalize_Scalars}. A special Makefile called
@code{Makefile.adalib} is provided to that effect and can be found in
the directory containing the GNAT library. The location of this
directory depends on the way the GNAT environment has been installed and can
be determined by means of the command:

@example
$ gnatls -v
@end example

The last entry in the object search path usually contains the
gnat library. This Makefile contains its own documentation and in
particular the set of instructions needed to rebuild a new library and
to use it.

@geindex Conditional compilation

@node Conditional Compilation,Mixed Language Programming,GNAT and Libraries,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model id47}@anchor{98}@anchor{gnat_ugn/the_gnat_compilation_model conditional-compilation}@anchor{16}
@section Conditional Compilation


This section presents some guidelines for modeling conditional compilation in Ada and describes the
gnatprep preprocessor utility.

@geindex Conditional compilation

@menu
* Modeling Conditional Compilation in Ada:: 
* Preprocessing with gnatprep:: 
* Integrated Preprocessing:: 

@end menu

@node Modeling Conditional Compilation in Ada,Preprocessing with gnatprep,,Conditional Compilation
@anchor{gnat_ugn/the_gnat_compilation_model modeling-conditional-compilation-in-ada}@anchor{99}@anchor{gnat_ugn/the_gnat_compilation_model id48}@anchor{9a}
@subsection Modeling Conditional Compilation in Ada


It is often necessary to arrange for a single source program
to serve multiple purposes, where it is compiled in different
ways to achieve these different goals. Some examples of the
need for this feature are


@itemize *

@item 
Adapting a program to a different hardware environment

@item 
Adapting a program to a different target architecture

@item 
Turning debugging features on and off

@item 
Arranging for a program to compile with different compilers
@end itemize

In C, or C++, the typical approach would be to use the preprocessor
that is defined as part of the language. The Ada language does not
contain such a feature. This is not an oversight, but rather a very
deliberate design decision, based on the experience that overuse of
the preprocessing features in C and C++ can result in programs that
are extremely difficult to maintain. For example, if we have ten
switches that can be on or off, this means that there are a thousand
separate programs, any one of which might not even be syntactically
correct, and even if syntactically correct, the resulting program
might not work correctly. Testing all combinations can quickly become
impossible.

Nevertheless, the need to tailor programs certainly exists, and in
this section we will discuss how this can
be achieved using Ada in general, and GNAT in particular.

@menu
* Use of Boolean Constants:: 
* Debugging - A Special Case:: 
* Conditionalizing Declarations:: 
* Use of Alternative Implementations:: 
* Preprocessing:: 

@end menu

@node Use of Boolean Constants,Debugging - A Special Case,,Modeling Conditional Compilation in Ada
@anchor{gnat_ugn/the_gnat_compilation_model id49}@anchor{9b}@anchor{gnat_ugn/the_gnat_compilation_model use-of-boolean-constants}@anchor{9c}
@subsubsection Use of Boolean Constants


In the case where the difference is simply which code
sequence is executed, the cleanest solution is to use Boolean
constants to control which code is executed.

@example
FP_Initialize_Required : constant Boolean := True;
...
if FP_Initialize_Required then
...
end if;
@end example

Not only will the code inside the @code{if} statement not be executed if
the constant Boolean is @code{False}, but it will also be completely
deleted from the program.
However, the code is only deleted after the @code{if} statement
has been checked for syntactic and semantic correctness.
(In contrast, with preprocessors the code is deleted before the
compiler ever gets to see it, so it is not checked until the switch
is turned on.)

@geindex Preprocessors (contrasted with conditional compilation)

Typically the Boolean constants will be in a separate package,
something like:

@example
package Config is
   FP_Initialize_Required : constant Boolean := True;
   Reset_Available        : constant Boolean := False;
   ...
end Config;
@end example

The @code{Config} package exists in multiple forms for the various targets,
with an appropriate script selecting the version of @code{Config} needed.
Then any other unit requiring conditional compilation can do a @emph{with}
of @code{Config} to make the constants visible.

@node Debugging - A Special Case,Conditionalizing Declarations,Use of Boolean Constants,Modeling Conditional Compilation in Ada
@anchor{gnat_ugn/the_gnat_compilation_model debugging-a-special-case}@anchor{9d}@anchor{gnat_ugn/the_gnat_compilation_model id50}@anchor{9e}
@subsubsection Debugging - A Special Case


A common use of conditional code is to execute statements (for example
dynamic checks, or output of intermediate results) under control of a
debug switch, so that the debugging behavior can be turned on and off.
This can be done using a Boolean constant to control whether the code
is active:

@example
if Debugging then
   Put_Line ("got to the first stage!");
end if;
@end example

or

@example
if Debugging and then Temperature > 999.0 then
   raise Temperature_Crazy;
end if;
@end example

@geindex pragma Assert

Since this is a common case, there are special features to deal with
this in a convenient manner. For the case of tests, Ada 2005 has added
a pragma @code{Assert} that can be used for such tests. This pragma is modeled
on the @code{Assert} pragma that has always been available in GNAT, so this
feature may be used with GNAT even if you are not using Ada 2005 features.
The use of pragma @code{Assert} is described in the
@cite{GNAT_Reference_Manual}, but as an
example, the last test could be written:

@example
pragma Assert (Temperature <= 999.0, "Temperature Crazy");
@end example

or simply

@example
pragma Assert (Temperature <= 999.0);
@end example

In both cases, if assertions are active and the temperature is excessive,
the exception @code{Assert_Failure} will be raised, with the given string in
the first case or a string indicating the location of the pragma in the second
case used as the exception message.

@geindex pragma Assertion_Policy

You can turn assertions on and off by using the @code{Assertion_Policy}
pragma.

@geindex -gnata switch

This is an Ada 2005 pragma which is implemented in all modes by
GNAT. Alternatively, you can use the @code{-gnata} switch
to enable assertions from the command line, which applies to
all versions of Ada.

@geindex pragma Debug

For the example above with the @code{Put_Line}, the GNAT-specific pragma
@code{Debug} can be used:

@example
pragma Debug (Put_Line ("got to the first stage!"));
@end example

If debug pragmas are enabled, the argument, which must be of the form of
a procedure call, is executed (in this case, @code{Put_Line} will be called).
Only one call can be present, but of course a special debugging procedure
containing any code you like can be included in the program and then
called in a pragma @code{Debug} argument as needed.

One advantage of pragma @code{Debug} over the @code{if Debugging then}
construct is that pragma @code{Debug} can appear in declarative contexts,
such as at the very beginning of a procedure, before local declarations have
been elaborated.

@geindex pragma Debug_Policy

Debug pragmas are enabled using either the @code{-gnata} switch that also
controls assertions, or with a separate Debug_Policy pragma.

The latter pragma is new in the Ada 2005 versions of GNAT (but it can be used
in Ada 95 and Ada 83 programs as well), and is analogous to
pragma @code{Assertion_Policy} to control assertions.

@code{Assertion_Policy} and @code{Debug_Policy} are configuration pragmas,
and thus they can appear in @code{gnat.adc} if you are not using a
project file, or in the file designated to contain configuration pragmas
in a project file.
They then apply to all subsequent compilations. In practice the use of
the @code{-gnata} switch is often the most convenient method of controlling
the status of these pragmas.

Note that a pragma is not a statement, so in contexts where a statement
sequence is required, you can't just write a pragma on its own. You have
to add a @code{null} statement.

@example
if ... then
   ... -- some statements
else
   pragma Assert (Num_Cases < 10);
   null;
end if;
@end example

@node Conditionalizing Declarations,Use of Alternative Implementations,Debugging - A Special Case,Modeling Conditional Compilation in Ada
@anchor{gnat_ugn/the_gnat_compilation_model conditionalizing-declarations}@anchor{9f}@anchor{gnat_ugn/the_gnat_compilation_model id51}@anchor{a0}
@subsubsection Conditionalizing Declarations


In some cases it may be necessary to conditionalize declarations to meet
different requirements. For example we might want a bit string whose length
is set to meet some hardware message requirement.

This may be possible using declare blocks controlled
by conditional constants:

@example
if Small_Machine then
   declare
      X : Bit_String (1 .. 10);
   begin
      ...
   end;
else
   declare
      X : Large_Bit_String (1 .. 1000);
   begin
      ...
   end;
end if;
@end example

Note that in this approach, both declarations are analyzed by the
compiler so this can only be used where both declarations are legal,
even though one of them will not be used.

Another approach is to define integer constants, e.g., @code{Bits_Per_Word},
or Boolean constants, e.g., @code{Little_Endian}, and then write declarations
that are parameterized by these constants. For example

@example
for Rec use
  Field1 at 0 range Boolean'Pos (Little_Endian) * 10 .. Bits_Per_Word;
end record;
@end example

If @code{Bits_Per_Word} is set to 32, this generates either

@example
for Rec use
  Field1 at 0 range 0 .. 32;
end record;
@end example

for the big endian case, or

@example
for Rec use record
    Field1 at 0 range 10 .. 32;
end record;
@end example

for the little endian case. Since a powerful subset of Ada expression
notation is usable for creating static constants, clever use of this
feature can often solve quite difficult problems in conditionalizing
compilation (note incidentally that in Ada 95, the little endian
constant was introduced as @code{System.Default_Bit_Order}, so you do not
need to define this one yourself).

@node Use of Alternative Implementations,Preprocessing,Conditionalizing Declarations,Modeling Conditional Compilation in Ada
@anchor{gnat_ugn/the_gnat_compilation_model use-of-alternative-implementations}@anchor{a1}@anchor{gnat_ugn/the_gnat_compilation_model id52}@anchor{a2}
@subsubsection Use of Alternative Implementations


In some cases, none of the approaches described above are adequate. This
can occur for example if the set of declarations required is radically
different for two different configurations.

In this situation, the official Ada way of dealing with conditionalizing
such code is to write separate units for the different cases. As long as
this does not result in excessive duplication of code, this can be done
without creating maintenance problems. The approach is to share common
code as far as possible, and then isolate the code and declarations
that are different. Subunits are often a convenient method for breaking
out a piece of a unit that is to be conditionalized, with separate files
for different versions of the subunit for different targets, where the
build script selects the right one to give to the compiler.

@geindex Subunits (and conditional compilation)

As an example, consider a situation where a new feature in Ada 2005
allows something to be done in a really nice way. But your code must be able
to compile with an Ada 95 compiler. Conceptually you want to say:

@example
if Ada_2005 then
   ... neat Ada 2005 code
else
   ... not quite as neat Ada 95 code
end if;
@end example

where @code{Ada_2005} is a Boolean constant.

But this won't work when @code{Ada_2005} is set to @code{False},
since the @code{then} clause will be illegal for an Ada 95 compiler.
(Recall that although such unreachable code would eventually be deleted
by the compiler, it still needs to be legal.  If it uses features
introduced in Ada 2005, it will be illegal in Ada 95.)

So instead we write

@example
procedure Insert is separate;
@end example

Then we have two files for the subunit @code{Insert}, with the two sets of
code.
If the package containing this is called @code{File_Queries}, then we might
have two files


@itemize *

@item 
@code{file_queries-insert-2005.adb}

@item 
@code{file_queries-insert-95.adb}
@end itemize

and the build script renames the appropriate file to @code{file_queries-insert.adb} and then carries out the compilation.

This can also be done with project files' naming schemes. For example:

@example
for body ("File_Queries.Insert") use "file_queries-insert-2005.ada";
@end example

Note also that with project files it is desirable to use a different extension
than @code{ads} / @code{adb} for alternative versions. Otherwise a naming
conflict may arise through another commonly used feature: to declare as part
of the project a set of directories containing all the sources obeying the
default naming scheme.

The use of alternative units is certainly feasible in all situations,
and for example the Ada part of the GNAT run-time is conditionalized
based on the target architecture using this approach. As a specific example,
consider the implementation of the AST feature in VMS. There is one
spec: @code{s-asthan.ads} which is the same for all architectures, and three
bodies:


@itemize *

@item 

@table @asis

@item @code{s-asthan.adb}

used for all non-VMS operating systems
@end table

@item 

@table @asis

@item @code{s-asthan-vms-alpha.adb}

used for VMS on the Alpha
@end table

@item 

@table @asis

@item @code{s-asthan-vms-ia64.adb}

used for VMS on the ia64
@end table
@end itemize

The dummy version @code{s-asthan.adb} simply raises exceptions noting that
this operating system feature is not available, and the two remaining
versions interface with the corresponding versions of VMS to provide
VMS-compatible AST handling. The GNAT build script knows the architecture
and operating system, and automatically selects the right version,
renaming it if necessary to @code{s-asthan.adb} before the run-time build.

Another style for arranging alternative implementations is through Ada's
access-to-subprogram facility.
In case some functionality is to be conditionally included,
you can declare an access-to-procedure variable @code{Ref} that is initialized
to designate a 'do nothing' procedure, and then invoke @code{Ref.all}
when appropriate.
In some library package, set @code{Ref} to @code{Proc'Access} for some
procedure @code{Proc} that performs the relevant processing.
The initialization only occurs if the library package is included in the
program.
The same idea can also be implemented using tagged types and dispatching
calls.

@node Preprocessing,,Use of Alternative Implementations,Modeling Conditional Compilation in Ada
@anchor{gnat_ugn/the_gnat_compilation_model preprocessing}@anchor{a3}@anchor{gnat_ugn/the_gnat_compilation_model id53}@anchor{a4}
@subsubsection Preprocessing


@geindex Preprocessing

Although it is quite possible to conditionalize code without the use of
C-style preprocessing, as described earlier in this section, it is
nevertheless convenient in some cases to use the C approach. Moreover,
older Ada compilers have often provided some preprocessing capability,
so legacy code may depend on this approach, even though it is not
standard.

To accommodate such use, GNAT provides a preprocessor (modeled to a large
extent on the various preprocessors that have been used
with legacy code on other compilers, to enable easier transition).

@geindex gnatprep

The preprocessor may be used in two separate modes. It can be used quite
separately from the compiler, to generate a separate output source file
that is then fed to the compiler as a separate step. This is the
@code{gnatprep} utility, whose use is fully described in
@ref{17,,Preprocessing with gnatprep}.

The preprocessing language allows such constructs as

@example
#if DEBUG or else (PRIORITY > 4) then
   sequence of declarations
#else
   completely different sequence of declarations
#end if;
@end example

The values of the symbols @code{DEBUG} and @code{PRIORITY} can be
defined either on the command line or in a separate file.

The other way of running the preprocessor is even closer to the C style and
often more convenient. In this approach the preprocessing is integrated into
the compilation process. The compiler is given the preprocessor input which
includes @code{#if} lines etc, and then the compiler carries out the
preprocessing internally and processes the resulting output.
For more details on this approach, see @ref{18,,Integrated Preprocessing}.

@node Preprocessing with gnatprep,Integrated Preprocessing,Modeling Conditional Compilation in Ada,Conditional Compilation
@anchor{gnat_ugn/the_gnat_compilation_model id54}@anchor{a5}@anchor{gnat_ugn/the_gnat_compilation_model preprocessing-with-gnatprep}@anchor{17}
@subsection Preprocessing with @code{gnatprep}


@geindex gnatprep

@geindex Preprocessing (gnatprep)

This section discusses how to use GNAT's @code{gnatprep} utility for simple
preprocessing.
Although designed for use with GNAT, @code{gnatprep} does not depend on any
special GNAT features.
For further discussion of conditional compilation in general, see
@ref{16,,Conditional Compilation}.

@menu
* Preprocessing Symbols:: 
* Using gnatprep:: 
* Switches for gnatprep:: 
* Form of Definitions File:: 
* Form of Input Text for gnatprep:: 

@end menu

@node Preprocessing Symbols,Using gnatprep,,Preprocessing with gnatprep
@anchor{gnat_ugn/the_gnat_compilation_model id55}@anchor{a6}@anchor{gnat_ugn/the_gnat_compilation_model preprocessing-symbols}@anchor{a7}
@subsubsection Preprocessing Symbols


Preprocessing symbols are defined in @emph{definition files} and referenced in the
sources to be preprocessed. A preprocessing symbol is an identifier, following
normal Ada (case-insensitive) rules for its syntax, with the restriction that
all characters need to be in the ASCII set (no accented letters).

@node Using gnatprep,Switches for gnatprep,Preprocessing Symbols,Preprocessing with gnatprep
@anchor{gnat_ugn/the_gnat_compilation_model using-gnatprep}@anchor{a8}@anchor{gnat_ugn/the_gnat_compilation_model id56}@anchor{a9}
@subsubsection Using @code{gnatprep}


To call @code{gnatprep} use:

@example
$ gnatprep [ switches ] infile outfile [ deffile ]
@end example

where


@itemize *

@item 

@table @asis

@item @emph{switches}

is an optional sequence of switches as described in the next section.
@end table

@item 

@table @asis

@item @emph{infile}

is the full name of the input file, which is an Ada source
file containing preprocessor directives.
@end table

@item 

@table @asis

@item @emph{outfile}

is the full name of the output file, which is an Ada source
in standard Ada form. When used with GNAT, this file name will
normally have an @code{ads} or @code{adb} suffix.
@end table

@item 

@table @asis

@item @code{deffile}

is the full name of a text file containing definitions of
preprocessing symbols to be referenced by the preprocessor. This argument is
optional, and can be replaced by the use of the @code{-D} switch.
@end table
@end itemize

@node Switches for gnatprep,Form of Definitions File,Using gnatprep,Preprocessing with gnatprep
@anchor{gnat_ugn/the_gnat_compilation_model switches-for-gnatprep}@anchor{aa}@anchor{gnat_ugn/the_gnat_compilation_model id57}@anchor{ab}
@subsubsection Switches for @code{gnatprep}


@geindex --version (gnatprep)


@table @asis

@item @code{--version}

Display Copyright and version, then exit disregarding all other options.
@end table

@geindex --help (gnatprep)


@table @asis

@item @code{--help}

If @code{--version} was not used, display usage and then exit disregarding
all other options.
@end table

@geindex -b (gnatprep)


@table @asis

@item @code{-b}

Causes both preprocessor lines and the lines deleted by
preprocessing to be replaced by blank lines in the output source file,
preserving line numbers in the output file.
@end table

@geindex -c (gnatprep)


@table @asis

@item @code{-c}

Causes both preprocessor lines and the lines deleted
by preprocessing to be retained in the output source as comments marked
with the special string @code{"--! "}. This option will result in line numbers
being preserved in the output file.
@end table

@geindex -C (gnatprep)


@table @asis

@item @code{-C}

Causes comments to be scanned. Normally comments are ignored by gnatprep.
If this option is specified, then comments are scanned and any $symbol
substitutions performed as in program text. This is particularly useful
when structured comments are used (e.g., for programs written in a
pre-2014 version of the SPARK Ada subset). Note that this switch is not
available when  doing integrated preprocessing (it would be useless in
this context since comments are ignored by the compiler in any case).
@end table

@geindex -D (gnatprep)


@table @asis

@item @code{-D@emph{symbol}[=@emph{value}]}

Defines a new preprocessing symbol with the specified value. If no value is given
on the command line, then symbol is considered to be @code{True}. This switch
can be used in place of a definition file.
@end table

@geindex -r (gnatprep)


@table @asis

@item @code{-r}

Causes a @code{Source_Reference} pragma to be generated that
references the original input file, so that error messages will use
the file name of this original file. The use of this switch implies
that preprocessor lines are not to be removed from the file, so its
use will force @code{-b} mode if @code{-c}
has not been specified explicitly.

Note that if the file to be preprocessed contains multiple units, then
it will be necessary to @code{gnatchop} the output file from
@code{gnatprep}. If a @code{Source_Reference} pragma is present
in the preprocessed file, it will be respected by
@code{gnatchop -r}
so that the final chopped files will correctly refer to the original
input source file for @code{gnatprep}.
@end table

@geindex -s (gnatprep)


@table @asis

@item @code{-s}

Causes a sorted list of symbol names and values to be
listed on the standard output file.
@end table

@geindex -T (gnatprep)


@table @asis

@item @code{-T}

Use LF as line terminators when writing files. By default the line terminator
of the host (LF under unix, CR/LF under Windows) is used.
@end table

@geindex -u (gnatprep)


@table @asis

@item @code{-u}

Causes undefined symbols to be treated as having the value FALSE in the context
of a preprocessor test. In the absence of this option, an undefined symbol in
a @code{#if} or @code{#elsif} test will be treated as an error.
@end table

@geindex -v (gnatprep)


@table @asis

@item @code{-v}

Verbose mode: generates more output about work done.
@end table

Note: if neither @code{-b} nor @code{-c} is present,
then preprocessor lines and
deleted lines are completely removed from the output, unless -r is
specified, in which case -b is assumed.

@node Form of Definitions File,Form of Input Text for gnatprep,Switches for gnatprep,Preprocessing with gnatprep
@anchor{gnat_ugn/the_gnat_compilation_model form-of-definitions-file}@anchor{ac}@anchor{gnat_ugn/the_gnat_compilation_model id58}@anchor{ad}
@subsubsection Form of Definitions File


The definitions file contains lines of the form:

@example
symbol := value
@end example

where @code{symbol} is a preprocessing symbol, and @code{value} is one of the following:


@itemize *

@item 
Empty, corresponding to a null substitution,

@item 
A string literal using normal Ada syntax, or

@item 
Any sequence of characters from the set @{letters, digits, period, underline@}.
@end itemize

Comment lines may also appear in the definitions file, starting with
the usual @code{--},
and comments may be added to the definitions lines.

@node Form of Input Text for gnatprep,,Form of Definitions File,Preprocessing with gnatprep
@anchor{gnat_ugn/the_gnat_compilation_model id59}@anchor{ae}@anchor{gnat_ugn/the_gnat_compilation_model form-of-input-text-for-gnatprep}@anchor{af}
@subsubsection Form of Input Text for @code{gnatprep}


The input text may contain preprocessor conditional inclusion lines,
as well as general symbol substitution sequences.

The preprocessor conditional inclusion commands have the form:

@example
#if <expression> [then]
   lines
#elsif <expression> [then]
   lines
#elsif <expression> [then]
   lines
...
#else
   lines
#end if;
@end example

In this example, <expression> is defined by the following grammar:

@example
<expression> ::=  <symbol>
<expression> ::=  <symbol> = "<value>"
<expression> ::=  <symbol> = <symbol>
<expression> ::=  <symbol> = <integer>
<expression> ::=  <symbol> > <integer>
<expression> ::=  <symbol> >= <integer>
<expression> ::=  <symbol> < <integer>
<expression> ::=  <symbol> <= <integer>
<expression> ::=  <symbol> 'Defined
<expression> ::=  not <expression>
<expression> ::=  <expression> and <expression>
<expression> ::=  <expression> or <expression>
<expression> ::=  <expression> and then <expression>
<expression> ::=  <expression> or else <expression>
<expression> ::=  ( <expression> )
@end example

Note the following restriction: it is not allowed to have "and" or "or"
following "not" in the same expression without parentheses. For example, this
is not allowed:

@example
not X or Y
@end example

This can be expressed instead as one of the following forms:

@example
(not X) or Y
not (X or Y)
@end example

For the first test (<expression> ::= <symbol>) the symbol must have
either the value true or false, that is to say the right-hand of the
symbol definition must be one of the (case-insensitive) literals
@code{True} or @code{False}. If the value is true, then the
corresponding lines are included, and if the value is false, they are
excluded.

When comparing a symbol to an integer, the integer is any non negative
literal integer as defined in the Ada Reference Manual, such as 3, 16#FF# or
2#11#. The symbol value must also be a non negative integer. Integer values
in the range 0 .. 2**31-1 are supported.

The test (<expression> ::= <symbol>'Defined) is true only if
the symbol has been defined in the definition file or by a @code{-D}
switch on the command line. Otherwise, the test is false.

The equality tests are case insensitive, as are all the preprocessor lines.

If the symbol referenced is not defined in the symbol definitions file,
then the effect depends on whether or not switch @code{-u}
is specified. If so, then the symbol is treated as if it had the value
false and the test fails. If this switch is not specified, then
it is an error to reference an undefined symbol. It is also an error to
reference a symbol that is defined with a value other than @code{True}
or @code{False}.

The use of the @code{not} operator inverts the sense of this logical test.
The @code{not} operator cannot be combined with the @code{or} or @code{and}
operators, without parentheses. For example, "if not X or Y then" is not
allowed, but "if (not X) or Y then" and "if not (X or Y) then" are.

The @code{then} keyword is optional as shown

The @code{#} must be the first non-blank character on a line, but
otherwise the format is free form. Spaces or tabs may appear between
the @code{#} and the keyword. The keywords and the symbols are case
insensitive as in normal Ada code. Comments may be used on a
preprocessor line, but other than that, no other tokens may appear on a
preprocessor line. Any number of @code{elsif} clauses can be present,
including none at all. The @code{else} is optional, as in Ada.

The @code{#} marking the start of a preprocessor line must be the first
non-blank character on the line, i.e., it must be preceded only by
spaces or horizontal tabs.

Symbol substitution outside of preprocessor lines is obtained by using
the sequence:

@example
$symbol
@end example

anywhere within a source line, except in a comment or within a
string literal. The identifier
following the @code{$} must match one of the symbols defined in the symbol
definition file, and the result is to substitute the value of the
symbol in place of @code{$symbol} in the output file.

Note that although the substitution of strings within a string literal
is not possible, it is possible to have a symbol whose defined value is
a string literal. So instead of setting XYZ to @code{hello} and writing:

@example
Header : String := "$XYZ";
@end example

you should set XYZ to @code{"hello"} and write:

@example
Header : String := $XYZ;
@end example

and then the substitution will occur as desired.

@node Integrated Preprocessing,,Preprocessing with gnatprep,Conditional Compilation
@anchor{gnat_ugn/the_gnat_compilation_model id60}@anchor{b0}@anchor{gnat_ugn/the_gnat_compilation_model integrated-preprocessing}@anchor{18}
@subsection Integrated Preprocessing


As noted above, a file to be preprocessed consists of Ada source code
in which preprocessing lines have been inserted. However,
instead of using @code{gnatprep} to explicitly preprocess a file as a separate
step before compilation, you can carry out the preprocessing implicitly
as part of compilation. Such @emph{integrated preprocessing}, which is the common
style with C, is performed when either or both of the following switches
are passed to the compiler:

@quotation


@itemize *

@item 
@code{-gnatep}, which specifies the @emph{preprocessor data file}.
This file dictates how the source files will be preprocessed (e.g., which
symbol definition files apply to which sources).

@item 
@code{-gnateD}, which defines values for preprocessing symbols.
@end itemize
@end quotation

Integrated preprocessing applies only to Ada source files, it is
not available for configuration pragma files.

With integrated preprocessing, the output from the preprocessor is not,
by default, written to any external file. Instead it is passed
internally to the compiler. To preserve the result of
preprocessing in a file, either run @code{gnatprep}
in standalone mode or else supply the @code{-gnateG} switch
(described below) to the compiler.

When using project files:

@quotation


@itemize *

@item 
the builder switch @code{-x} should be used if any Ada source is
compiled with @code{gnatep=}, so that the compiler finds the
@emph{preprocessor data file}.

@item 
the preprocessing data file and the symbol definition files should be
located in the source directories of the project.
@end itemize
@end quotation

Note that the @code{gnatmake} switch @code{-m} will almost
always trigger recompilation for sources that are preprocessed,
because @code{gnatmake} cannot compute the checksum of the source after
preprocessing.

The actual preprocessing function is described in detail in
@ref{17,,Preprocessing with gnatprep}. This section explains the switches
that relate to integrated preprocessing.

@geindex -gnatep (gcc)


@table @asis

@item @code{-gnatep=@emph{preprocessor_data_file}}

This switch specifies the file name (without directory
information) of the preprocessor data file. Either place this file
in one of the source directories, or, when using project
files, reference the project file's directory via the
@code{project_name'Project_Dir} project attribute; e.g:

@quotation

@example
project Prj is
   package Compiler is
      for Switches ("Ada") use
        ("-gnatep=" & Prj'Project_Dir & "prep.def");
   end Compiler;
end Prj;
@end example
@end quotation

A preprocessor data file is a text file that contains @emph{preprocessor
control lines}.  A preprocessor control line directs the preprocessing of
either a particular source file, or, analogous to @code{others} in Ada,
all sources not specified elsewhere in  the preprocessor data file.
A preprocessor control line
can optionally identify a @emph{definition file} that assigns values to
preprocessor symbols, as well as a list of switches that relate to
preprocessing.
Empty lines and comments (using Ada syntax) are also permitted, with no
semantic effect.

Here's an example of a preprocessor data file:

@quotation

@example
"toto.adb"  "prep.def" -u
--  Preprocess toto.adb, using definition file prep.def
--  Undefined symbols are treated as False

* -c -DVERSION=V101
--  Preprocess all other sources without using a definition file
--  Suppressed lined are commented
--  Symbol VERSION has the value V101

"tata.adb" "prep2.def" -s
--  Preprocess tata.adb, using definition file prep2.def
--  List all symbols with their values
@end example
@end quotation

A preprocessor control line has the following syntax:

@quotation

@example
<preprocessor_control_line> ::=
   <preprocessor_input> [ <definition_file_name> ] @{ <switch> @}

<preprocessor_input> ::= <source_file_name> | '*'

<definition_file_name> ::= <string_literal>

<source_file_name> := <string_literal>

<switch> := (See below for list)
@end example
@end quotation

Thus  each preprocessor control line starts with either a literal string or
the character '*':


@itemize *

@item 
A literal string is the file name (without directory information) of the source
file that will be input to the preprocessor.

@item 
The character '*' is a wild-card indicator; the additional parameters on the line
indicate the preprocessing for all the sources
that are not specified explicitly on other lines (the order of the lines is not
significant).
@end itemize

It is an error to have two lines with the same file name or two
lines starting with the character '*'.

After the file name or '*', an optional literal string specifies the name of
the definition file to be used for preprocessing
(@ref{ac,,Form of Definitions File}). The definition files are found by the
compiler in one of the source directories. In some cases, when compiling
a source in a directory other than the current directory, if the definition
file is in the current directory, it may be necessary to add the current
directory as a source directory through the @code{-I} switch; otherwise
the compiler would not find the definition file.

Finally, switches similar to those of @code{gnatprep} may optionally appear:


@table @asis

@item @code{-b}

Causes both preprocessor lines and the lines deleted by
preprocessing to be replaced by blank lines, preserving the line number.
This switch is always implied; however, if specified after @code{-c}
it cancels the effect of @code{-c}.

@item @code{-c}

Causes both preprocessor lines and the lines deleted
by preprocessing to be retained as comments marked
with the special string '@cite{--!}'.

@item @code{-D@emph{symbol}=@emph{new_value}}

Define or redefine @code{symbol} to have @code{new_value} as its value.
The permitted form for @code{symbol} is either an Ada identifier, or any Ada reserved word
aside from @code{if},
@code{else}, @code{elsif}, @code{end}, @code{and}, @code{or} and @code{then}.
The permitted form for @code{new_value} is a literal string, an Ada identifier or any Ada reserved
word. A symbol declared with this switch replaces a symbol with the
same name defined in a definition file.

@item @code{-s}

Causes a sorted list of symbol names and values to be
listed on the standard output file.

@item @code{-u}

Causes undefined symbols to be treated as having the value @code{FALSE}
in the context
of a preprocessor test. In the absence of this option, an undefined symbol in
a @code{#if} or @code{#elsif} test will be treated as an error.
@end table
@end table

@geindex -gnateD (gcc)


@table @asis

@item @code{-gnateD@emph{symbol}[=@emph{new_value}]}

Define or redefine @code{symbol} to have @code{new_value} as its value. If no value
is supplied, then the value of @code{symbol} is @code{True}.
The form of @code{symbol} is an identifier, following normal Ada (case-insensitive)
rules for its syntax, and @code{new_value} is either an arbitrary string between double
quotes or any sequence (including an empty sequence) of characters from the
set (letters, digits, period, underline).
Ada reserved words may be used as symbols, with the exceptions of @code{if},
@code{else}, @code{elsif}, @code{end}, @code{and}, @code{or} and @code{then}.

Examples:

@quotation

@example
-gnateDToto=Tata
-gnateDFoo
-gnateDFoo=\"Foo-Bar\"
@end example
@end quotation

A symbol declared with this switch on the command line replaces a
symbol with the same name either in a definition file or specified with a
switch @code{-D} in the preprocessor data file.

This switch is similar to switch @code{-D} of @code{gnatprep}.

@item @code{-gnateG}

When integrated preprocessing is performed on source file @code{filename.extension},
create or overwrite @code{filename.extension.prep} to contain
the result of the preprocessing.
For example if the source file is @code{foo.adb} then
the output file will be @code{foo.adb.prep}.
@end table

@node Mixed Language Programming,GNAT and Other Compilation Models,Conditional Compilation,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model mixed-language-programming}@anchor{44}@anchor{gnat_ugn/the_gnat_compilation_model id61}@anchor{b1}
@section Mixed Language Programming


@geindex Mixed Language Programming

This section describes how to develop a mixed-language program,
with a focus on combining Ada with C or C++.

@menu
* Interfacing to C:: 
* Calling Conventions:: 
* Building Mixed Ada and C++ Programs:: 
* Generating Ada Bindings for C and C++ headers:: 
* Generating C Headers for Ada Specifications:: 

@end menu

@node Interfacing to C,Calling Conventions,,Mixed Language Programming
@anchor{gnat_ugn/the_gnat_compilation_model interfacing-to-c}@anchor{b2}@anchor{gnat_ugn/the_gnat_compilation_model id62}@anchor{b3}
@subsection Interfacing to C


Interfacing Ada with a foreign language such as C involves using
compiler directives to import and/or export entity definitions in each
language -- using @code{extern} statements in C, for instance, and the
@code{Import}, @code{Export}, and @code{Convention} pragmas in Ada.
A full treatment of these topics is provided in Appendix B, section 1
of the Ada Reference Manual.

There are two ways to build a program using GNAT that contains some Ada
sources and some foreign language sources, depending on whether or not
the main subprogram is written in Ada.  Here is a source example with
the main subprogram in Ada:

@example
/* file1.c */
#include <stdio.h>

void print_num (int num)
@{
  printf ("num is %d.\\n", num);
  return;
@}
@end example

@example
/* file2.c */

/* num_from_Ada is declared in my_main.adb */
extern int num_from_Ada;

int get_num (void)
@{
  return num_from_Ada;
@}
@end example

@example
--  my_main.adb
procedure My_Main is

   --  Declare then export an Integer entity called num_from_Ada
   My_Num : Integer := 10;
   pragma Export (C, My_Num, "num_from_Ada");

   --  Declare an Ada function spec for Get_Num, then use
   --  C function get_num for the implementation.
   function Get_Num return Integer;
   pragma Import (C, Get_Num, "get_num");

   --  Declare an Ada procedure spec for Print_Num, then use
   --  C function print_num for the implementation.
   procedure Print_Num (Num : Integer);
   pragma Import (C, Print_Num, "print_num");

begin
   Print_Num (Get_Num);
end My_Main;
@end example

To build this example:


@itemize *

@item 
First compile the foreign language files to
generate object files:

@example
$ gcc -c file1.c
$ gcc -c file2.c
@end example

@item 
Then, compile the Ada units to produce a set of object files and ALI
files:

@example
$ gnatmake -c my_main.adb
@end example

@item 
Run the Ada binder on the Ada main program:

@example
$ gnatbind my_main.ali
@end example

@item 
Link the Ada main program, the Ada objects and the other language
objects:

@example
$ gnatlink my_main.ali file1.o file2.o
@end example
@end itemize

The last three steps can be grouped in a single command:

@example
$ gnatmake my_main.adb -largs file1.o file2.o
@end example

@geindex Binder output file

If the main program is in a language other than Ada, then you may have
more than one entry point into the Ada subsystem. You must use a special
binder option to generate callable routines that initialize and
finalize the Ada units (@ref{b4,,Binding with Non-Ada Main Programs}).
Calls to the initialization and finalization routines must be inserted
in the main program, or some other appropriate point in the code. The
call to initialize the Ada units must occur before the first Ada
subprogram is called, and the call to finalize the Ada units must occur
after the last Ada subprogram returns. The binder will place the
initialization and finalization subprograms into the
@code{b~xxx.adb} file where they can be accessed by your C
sources.  To illustrate, we have the following example:

@example
/* main.c */
extern void adainit (void);
extern void adafinal (void);
extern int add (int, int);
extern int sub (int, int);

int main (int argc, char *argv[])
@{
   int a = 21, b = 7;

   adainit();

   /* Should print "21 + 7 = 28" */
   printf ("%d + %d = %d\\n", a, b, add (a, b));

   /* Should print "21 - 7 = 14" */
   printf ("%d - %d = %d\\n", a, b, sub (a, b));

   adafinal();
@}
@end example

@example
--  unit1.ads
package Unit1 is
   function Add (A, B : Integer) return Integer;
   pragma Export (C, Add, "add");
end Unit1;
@end example

@example
--  unit1.adb
package body Unit1 is
   function Add (A, B : Integer) return Integer is
   begin
      return A + B;
   end Add;
end Unit1;
@end example

@example
--  unit2.ads
package Unit2 is
   function Sub (A, B : Integer) return Integer;
   pragma Export (C, Sub, "sub");
end Unit2;
@end example

@example
--  unit2.adb
package body Unit2 is
   function Sub (A, B : Integer) return Integer is
   begin
      return A - B;
   end Sub;
end Unit2;
@end example

The build procedure for this application is similar to the last
example's:


@itemize *

@item 
First, compile the foreign language files to generate object files:

@example
$ gcc -c main.c
@end example

@item 
Next, compile the Ada units to produce a set of object files and ALI
files:

@example
$ gnatmake -c unit1.adb
$ gnatmake -c unit2.adb
@end example

@item 
Run the Ada binder on every generated ALI file.  Make sure to use the
@code{-n} option to specify a foreign main program:

@example
$ gnatbind -n unit1.ali unit2.ali
@end example

@item 
Link the Ada main program, the Ada objects and the foreign language
objects. You need only list the last ALI file here:

@example
$ gnatlink unit2.ali main.o -o exec_file
@end example

This procedure yields a binary executable called @code{exec_file}.
@end itemize

Depending on the circumstances (for example when your non-Ada main object
does not provide symbol @code{main}), you may also need to instruct the
GNAT linker not to include the standard startup objects by passing the
@code{-nostartfiles} switch to @code{gnatlink}.

@node Calling Conventions,Building Mixed Ada and C++ Programs,Interfacing to C,Mixed Language Programming
@anchor{gnat_ugn/the_gnat_compilation_model calling-conventions}@anchor{b5}@anchor{gnat_ugn/the_gnat_compilation_model id63}@anchor{b6}
@subsection Calling Conventions


@geindex Foreign Languages

@geindex Calling Conventions

GNAT follows standard calling sequence conventions and will thus interface
to any other language that also follows these conventions. The following
Convention identifiers are recognized by GNAT:

@geindex Interfacing to Ada

@geindex Other Ada compilers

@geindex Convention Ada


@table @asis

@item @code{Ada}

This indicates that the standard Ada calling sequence will be
used and all Ada data items may be passed without any limitations in the
case where GNAT is used to generate both the caller and callee. It is also
possible to mix GNAT generated code and code generated by another Ada
compiler. In this case, the data types should be restricted to simple
cases, including primitive types. Whether complex data types can be passed
depends on the situation. Probably it is safe to pass simple arrays, such
as arrays of integers or floats. Records may or may not work, depending
on whether both compilers lay them out identically. Complex structures
involving variant records, access parameters, tasks, or protected types,
are unlikely to be able to be passed.

Note that in the case of GNAT running
on a platform that supports HP Ada 83, a higher degree of compatibility
can be guaranteed, and in particular records are laid out in an identical
manner in the two compilers. Note also that if output from two different
compilers is mixed, the program is responsible for dealing with elaboration
issues. Probably the safest approach is to write the main program in the
version of Ada other than GNAT, so that it takes care of its own elaboration
requirements, and then call the GNAT-generated adainit procedure to ensure
elaboration of the GNAT components. Consult the documentation of the other
Ada compiler for further details on elaboration.

However, it is not possible to mix the tasking run time of GNAT and
HP Ada 83, All the tasking operations must either be entirely within
GNAT compiled sections of the program, or entirely within HP Ada 83
compiled sections of the program.
@end table

@geindex Interfacing to Assembly

@geindex Convention Assembler


@table @asis

@item @code{Assembler}

Specifies assembler as the convention. In practice this has the
same effect as convention Ada (but is not equivalent in the sense of being
considered the same convention).
@end table

@geindex Convention Asm

@geindex Asm


@table @asis

@item @code{Asm}

Equivalent to Assembler.

@geindex Interfacing to COBOL

@geindex Convention COBOL
@end table

@geindex COBOL


@table @asis

@item @code{COBOL}

Data will be passed according to the conventions described
in section B.4 of the Ada Reference Manual.
@end table

@geindex C

@geindex Interfacing to C

@geindex Convention C


@table @asis

@item @code{C}

Data will be passed according to the conventions described
in section B.3 of the Ada Reference Manual.

A note on interfacing to a C 'varargs' function:

@quotation

@geindex C varargs function

@geindex Interfacing to C varargs function

@geindex varargs function interfaces

In C, @code{varargs} allows a function to take a variable number of
arguments. There is no direct equivalent in this to Ada. One
approach that can be used is to create a C wrapper for each
different profile and then interface to this C wrapper. For
example, to print an @code{int} value using @code{printf},
create a C function @code{printfi} that takes two arguments, a
pointer to a string and an int, and calls @code{printf}.
Then in the Ada program, use pragma @code{Import} to
interface to @code{printfi}.

It may work on some platforms to directly interface to
a @code{varargs} function by providing a specific Ada profile
for a particular call. However, this does not work on
all platforms, since there is no guarantee that the
calling sequence for a two argument normal C function
is the same as for calling a @code{varargs} C function with
the same two arguments.
@end quotation
@end table

@geindex Convention Default

@geindex Default


@table @asis

@item @code{Default}

Equivalent to C.
@end table

@geindex Convention External

@geindex External


@table @asis

@item @code{External}

Equivalent to C.
@end table

@geindex C++

@geindex Interfacing to C++

@geindex Convention C++


@table @asis

@item @code{C_Plus_Plus} (or @code{CPP})

This stands for C++. For most purposes this is identical to C.
See the separate description of the specialized GNAT pragmas relating to
C++ interfacing for further details.
@end table

@geindex Fortran

@geindex Interfacing to Fortran

@geindex Convention Fortran


@table @asis

@item @code{Fortran}

Data will be passed according to the conventions described
in section B.5 of the Ada Reference Manual.

@item @code{Intrinsic}

This applies to an intrinsic operation, as defined in the Ada
Reference Manual. If a pragma Import (Intrinsic) applies to a subprogram,
this means that the body of the subprogram is provided by the compiler itself,
usually by means of an efficient code sequence, and that the user does not
supply an explicit body for it. In an application program, the pragma may
be applied to the following sets of names:


@itemize *

@item 
Rotate_Left, Rotate_Right, Shift_Left, Shift_Right, Shift_Right_Arithmetic.
The corresponding subprogram declaration must have
two formal parameters. The
first one must be a signed integer type or a modular type with a binary
modulus, and the second parameter must be of type Natural.
The return type must be the same as the type of the first argument. The size
of this type can only be 8, 16, 32, or 64.

@item 
Binary arithmetic operators: '+', '-', '*', '/'.
The corresponding operator declaration must have parameters and result type
that have the same root numeric type (for example, all three are long_float
types). This simplifies the definition of operations that use type checking
to perform dimensional checks:
@end itemize

@example
  type Distance is new Long_Float;
  type Time     is new Long_Float;
  type Velocity is new Long_Float;
  function "/" (D : Distance; T : Time)
    return Velocity;
  pragma Import (Intrinsic, "/");

This common idiom is often programmed with a generic definition and an
explicit body. The pragma makes it simpler to introduce such declarations.
It incurs no overhead in compilation time or code size, because it is
implemented as a single machine instruction.
@end example


@itemize *

@item 
General subprogram entities. This is used  to bind an Ada subprogram
declaration to
a compiler builtin by name with back-ends where such interfaces are
available. A typical example is the set of @code{__builtin} functions
exposed by the GCC back-end, as in the following example:

@example
function builtin_sqrt (F : Float) return Float;
pragma Import (Intrinsic, builtin_sqrt, "__builtin_sqrtf");
@end example

Most of the GCC builtins are accessible this way, and as for other
import conventions (e.g. C), it is the user's responsibility to ensure
that the Ada subprogram profile matches the underlying builtin
expectations.
@end itemize
@end table

@geindex Stdcall

@geindex Convention Stdcall


@table @asis

@item @code{Stdcall}

This is relevant only to Windows implementations of GNAT,
and specifies that the @code{Stdcall} calling sequence will be used,
as defined by the NT API. Nevertheless, to ease building
cross-platform bindings this convention will be handled as a @code{C} calling
convention on non-Windows platforms.
@end table

@geindex DLL

@geindex Convention DLL


@table @asis

@item @code{DLL}

This is equivalent to @code{Stdcall}.
@end table

@geindex Win32

@geindex Convention Win32


@table @asis

@item @code{Win32}

This is equivalent to @code{Stdcall}.
@end table

@geindex Stubbed

@geindex Convention Stubbed


@table @asis

@item @code{Stubbed}

This is a special convention that indicates that the compiler
should provide a stub body that raises @code{Program_Error}.
@end table

GNAT additionally provides a useful pragma @code{Convention_Identifier}
that can be used to parameterize conventions and allow additional synonyms
to be specified. For example if you have legacy code in which the convention
identifier Fortran77 was used for Fortran, you can use the configuration
pragma:

@example
pragma Convention_Identifier (Fortran77, Fortran);
@end example

And from now on the identifier Fortran77 may be used as a convention
identifier (for example in an @code{Import} pragma) with the same
meaning as Fortran.

@node Building Mixed Ada and C++ Programs,Generating Ada Bindings for C and C++ headers,Calling Conventions,Mixed Language Programming
@anchor{gnat_ugn/the_gnat_compilation_model id64}@anchor{b7}@anchor{gnat_ugn/the_gnat_compilation_model building-mixed-ada-and-c-programs}@anchor{b8}
@subsection Building Mixed Ada and C++ Programs


A programmer inexperienced with mixed-language development may find that
building an application containing both Ada and C++ code can be a
challenge.  This section gives a few hints that should make this task easier.

@menu
* Interfacing to C++:: 
* Linking a Mixed C++ & Ada Program:: 
* A Simple Example:: 
* Interfacing with C++ constructors:: 
* Interfacing with C++ at the Class Level:: 

@end menu

@node Interfacing to C++,Linking a Mixed C++ & Ada Program,,Building Mixed Ada and C++ Programs
@anchor{gnat_ugn/the_gnat_compilation_model id65}@anchor{b9}@anchor{gnat_ugn/the_gnat_compilation_model id66}@anchor{ba}
@subsubsection Interfacing to C++


GNAT supports interfacing with the G++ compiler (or any C++ compiler
generating code that is compatible with the G++ Application Binary
Interface ---see @indicateurl{http://www.codesourcery.com/archives/cxx-abi}).

Interfacing can be done at 3 levels: simple data, subprograms, and
classes. In the first two cases, GNAT offers a specific @code{Convention C_Plus_Plus}
(or @code{CPP}) that behaves exactly like @code{Convention C}.
Usually, C++ mangles the names of subprograms. To generate proper mangled
names automatically, see @ref{19,,Generating Ada Bindings for C and C++ headers}).
This problem can also be addressed manually in two ways:


@itemize *

@item 
by modifying the C++ code in order to force a C convention using
the @code{extern "C"} syntax.

@item 
by figuring out the mangled name (using e.g. @code{nm}) and using it as the
Link_Name argument of the pragma import.
@end itemize

Interfacing at the class level can be achieved by using the GNAT specific
pragmas such as @code{CPP_Constructor}.  See the @cite{GNAT_Reference_Manual} for additional information.

@node Linking a Mixed C++ & Ada Program,A Simple Example,Interfacing to C++,Building Mixed Ada and C++ Programs
@anchor{gnat_ugn/the_gnat_compilation_model linking-a-mixed-c-ada-program}@anchor{bb}@anchor{gnat_ugn/the_gnat_compilation_model linking-a-mixed-c-and-ada-program}@anchor{bc}
@subsubsection Linking a Mixed C++ & Ada Program


Usually the linker of the C++ development system must be used to link
mixed applications because most C++ systems will resolve elaboration
issues (such as calling constructors on global class instances)
transparently during the link phase. GNAT has been adapted to ease the
use of a foreign linker for the last phase. Three cases can be
considered:


@itemize *

@item 
Using GNAT and G++ (GNU C++ compiler) from the same GCC installation:
The C++ linker can simply be called by using the C++ specific driver
called @code{g++}.

Note that if the C++ code uses inline functions, you will need to
compile your C++ code with the @code{-fkeep-inline-functions} switch in
order to provide an existing function implementation that the Ada code can
link with.

@example
$ g++ -c -fkeep-inline-functions file1.C
$ g++ -c -fkeep-inline-functions file2.C
$ gnatmake ada_unit -largs file1.o file2.o --LINK=g++
@end example

@item 
Using GNAT and G++ from two different GCC installations: If both
compilers are on the :envvar`PATH`, the previous method may be used. It is
important to note that environment variables such as
@geindex C_INCLUDE_PATH
@geindex environment variable; C_INCLUDE_PATH
@code{C_INCLUDE_PATH}, 
@geindex GCC_EXEC_PREFIX
@geindex environment variable; GCC_EXEC_PREFIX
@code{GCC_EXEC_PREFIX},
@geindex BINUTILS_ROOT
@geindex environment variable; BINUTILS_ROOT
@code{BINUTILS_ROOT}, and
@geindex GCC_ROOT
@geindex environment variable; GCC_ROOT
@code{GCC_ROOT} will affect both compilers
at the same time and may make one of the two compilers operate
improperly if set during invocation of the wrong compiler.  It is also
very important that the linker uses the proper @code{libgcc.a} GCC
library -- that is, the one from the C++ compiler installation. The
implicit link command as suggested in the @code{gnatmake} command
from the former example can be replaced by an explicit link command with
the full-verbosity option in order to verify which library is used:

@example
$ gnatbind ada_unit
$ gnatlink -v -v ada_unit file1.o file2.o --LINK=c++
@end example

If there is a problem due to interfering environment variables, it can
be worked around by using an intermediate script. The following example
shows the proper script to use when GNAT has not been installed at its
default location and g++ has been installed at its default location:

@example
$ cat ./my_script
#!/bin/sh
unset BINUTILS_ROOT
unset GCC_ROOT
c++ $*
$ gnatlink -v -v ada_unit file1.o file2.o --LINK=./my_script
@end example

@item 
Using a non-GNU C++ compiler: The commands previously described can be
used to insure that the C++ linker is used. Nonetheless, you need to add
a few more parameters to the link command line, depending on the exception
mechanism used.

If the @code{setjmp} / @code{longjmp} exception mechanism is used, only the paths
to the @code{libgcc} libraries are required:

@example
$ cat ./my_script
#!/bin/sh
CC $* gcc -print-file-name=libgcc.a gcc -print-file-name=libgcc_eh.a
$ gnatlink ada_unit file1.o file2.o --LINK=./my_script
@end example

where CC is the name of the non-GNU C++ compiler.

If the "zero cost" exception mechanism is used, and the platform
supports automatic registration of exception tables (e.g., Solaris),
paths to more objects are required:

@example
$ cat ./my_script
#!/bin/sh
CC gcc -print-file-name=crtbegin.o $* \\
gcc -print-file-name=libgcc.a gcc -print-file-name=libgcc_eh.a \\
gcc -print-file-name=crtend.o
$ gnatlink ada_unit file1.o file2.o --LINK=./my_script
@end example

If the "zero cost exception" mechanism is used, and the platform
doesn't support automatic registration of exception tables (e.g., HP-UX
or AIX), the simple approach described above will not work and
a pre-linking phase using GNAT will be necessary.
@end itemize

Another alternative is to use the @code{gprbuild} multi-language builder
which has a large knowledge base and knows how to link Ada and C++ code
together automatically in most cases.

@node A Simple Example,Interfacing with C++ constructors,Linking a Mixed C++ & Ada Program,Building Mixed Ada and C++ Programs
@anchor{gnat_ugn/the_gnat_compilation_model id67}@anchor{bd}@anchor{gnat_ugn/the_gnat_compilation_model a-simple-example}@anchor{be}
@subsubsection A Simple Example


The following example, provided as part of the GNAT examples, shows how
to achieve procedural interfacing between Ada and C++ in both
directions. The C++ class A has two methods. The first method is exported
to Ada by the means of an extern C wrapper function. The second method
calls an Ada subprogram. On the Ada side, The C++ calls are modelled by
a limited record with a layout comparable to the C++ class. The Ada
subprogram, in turn, calls the C++ method. So, starting from the C++
main program, the process passes back and forth between the two
languages.

Here are the compilation commands:

@example
$ gnatmake -c simple_cpp_interface
$ g++ -c cpp_main.C
$ g++ -c ex7.C
$ gnatbind -n simple_cpp_interface
$ gnatlink simple_cpp_interface -o cpp_main --LINK=g++ -lstdc++ ex7.o cpp_main.o
@end example

Here are the corresponding sources:

@example
//cpp_main.C

#include "ex7.h"

extern "C" @{
  void adainit (void);
  void adafinal (void);
  void method1 (A *t);
@}

void method1 (A *t)
@{
  t->method1 ();
@}

int main ()
@{
  A obj;
  adainit ();
  obj.method2 (3030);
  adafinal ();
@}
@end example

@example
//ex7.h

class Origin @{
 public:
  int o_value;
@};
class A : public Origin @{
 public:
  void method1 (void);
  void method2 (int v);
  A();
  int   a_value;
@};
@end example

@example
//ex7.C

#include "ex7.h"
#include <stdio.h>

extern "C" @{ void ada_method2 (A *t, int v);@}

void A::method1 (void)
@{
  a_value = 2020;
  printf ("in A::method1, a_value = %d \\n",a_value);
@}

void A::method2 (int v)
@{
   ada_method2 (this, v);
   printf ("in A::method2, a_value = %d \\n",a_value);
@}

A::A(void)
@{
   a_value = 1010;
  printf ("in A::A, a_value = %d \\n",a_value);
@}
@end example

@example
-- simple_cpp_interface.ads
with System;
package Simple_Cpp_Interface is
   type A is limited
      record
         Vptr    : System.Address;
         O_Value : Integer;
         A_Value : Integer;
      end record;
   pragma Convention (C, A);

   procedure Method1 (This : in out A);
   pragma Import (C, Method1);

   procedure Ada_Method2 (This : in out A; V : Integer);
   pragma Export (C, Ada_Method2);

end Simple_Cpp_Interface;
@end example

@example
-- simple_cpp_interface.adb
package body Simple_Cpp_Interface is

   procedure Ada_Method2 (This : in out A; V : Integer) is
   begin
      Method1 (This);
      This.A_Value := V;
   end Ada_Method2;

end Simple_Cpp_Interface;
@end example

@node Interfacing with C++ constructors,Interfacing with C++ at the Class Level,A Simple Example,Building Mixed Ada and C++ Programs
@anchor{gnat_ugn/the_gnat_compilation_model id68}@anchor{bf}@anchor{gnat_ugn/the_gnat_compilation_model interfacing-with-c-constructors}@anchor{c0}
@subsubsection Interfacing with C++ constructors


In order to interface with C++ constructors GNAT provides the
@code{pragma CPP_Constructor} (see the @cite{GNAT_Reference_Manual}
for additional information).
In this section we present some common uses of C++ constructors
in mixed-languages programs in GNAT.

Let us assume that we need to interface with the following
C++ class:

@example
class Root @{
public:
  int  a_value;
  int  b_value;
  virtual int Get_Value ();
  Root();              // Default constructor
  Root(int v);         // 1st non-default constructor
  Root(int v, int w);  // 2nd non-default constructor
@};
@end example

For this purpose we can write the following package spec (further
information on how to build this spec is available in
@ref{c1,,Interfacing with C++ at the Class Level} and
@ref{19,,Generating Ada Bindings for C and C++ headers}).

@example
with Interfaces.C; use Interfaces.C;
package Pkg_Root is
  type Root is tagged limited record
     A_Value : int;
     B_Value : int;
  end record;
  pragma Import (CPP, Root);

  function Get_Value (Obj : Root) return int;
  pragma Import (CPP, Get_Value);

  function Constructor return Root;
  pragma Cpp_Constructor (Constructor, "_ZN4RootC1Ev");

  function Constructor (v : Integer) return Root;
  pragma Cpp_Constructor (Constructor, "_ZN4RootC1Ei");

  function Constructor (v, w : Integer) return Root;
  pragma Cpp_Constructor (Constructor, "_ZN4RootC1Eii");
end Pkg_Root;
@end example

On the Ada side the constructor is represented by a function (whose
name is arbitrary) that returns the classwide type corresponding to
the imported C++ class. Although the constructor is described as a
function, it is typically a procedure with an extra implicit argument
(the object being initialized) at the implementation level. GNAT
issues the appropriate call, whatever it is, to get the object
properly initialized.

Constructors can only appear in the following contexts:


@itemize *

@item 
On the right side of an initialization of an object of type @code{T}.

@item 
On the right side of an initialization of a record component of type @code{T}.

@item 
In an Ada 2005 limited aggregate.

@item 
In an Ada 2005 nested limited aggregate.

@item 
In an Ada 2005 limited aggregate that initializes an object built in
place by an extended return statement.
@end itemize

In a declaration of an object whose type is a class imported from C++,
either the default C++ constructor is implicitly called by GNAT, or
else the required C++ constructor must be explicitly called in the
expression that initializes the object. For example:

@example
Obj1 : Root;
Obj2 : Root := Constructor;
Obj3 : Root := Constructor (v => 10);
Obj4 : Root := Constructor (30, 40);
@end example

The first two declarations are equivalent: in both cases the default C++
constructor is invoked (in the former case the call to the constructor is
implicit, and in the latter case the call is explicit in the object
declaration). @code{Obj3} is initialized by the C++ non-default constructor
that takes an integer argument, and @code{Obj4} is initialized by the
non-default C++ constructor that takes two integers.

Let us derive the imported C++ class in the Ada side. For example:

@example
type DT is new Root with record
   C_Value : Natural := 2009;
end record;
@end example

In this case the components DT inherited from the C++ side must be
initialized by a C++ constructor, and the additional Ada components
of type DT are initialized by GNAT. The initialization of such an
object is done either by default, or by means of a function returning
an aggregate of type DT, or by means of an extension aggregate.

@example
Obj5 : DT;
Obj6 : DT := Function_Returning_DT (50);
Obj7 : DT := (Constructor (30,40) with C_Value => 50);
@end example

The declaration of @code{Obj5} invokes the default constructors: the
C++ default constructor of the parent type takes care of the initialization
of the components inherited from Root, and GNAT takes care of the default
initialization of the additional Ada components of type DT (that is,
@code{C_Value} is initialized to value 2009). The order of invocation of
the constructors is consistent with the order of elaboration required by
Ada and C++. That is, the constructor of the parent type is always called
before the constructor of the derived type.

Let us now consider a record that has components whose type is imported
from C++. For example:

@example
type Rec1 is limited record
   Data1 : Root := Constructor (10);
   Value : Natural := 1000;
end record;

type Rec2 (D : Integer := 20) is limited record
   Rec   : Rec1;
   Data2 : Root := Constructor (D, 30);
end record;
@end example

The initialization of an object of type @code{Rec2} will call the
non-default C++ constructors specified for the imported components.
For example:

@example
Obj8 : Rec2 (40);
@end example

Using Ada 2005 we can use limited aggregates to initialize an object
invoking C++ constructors that differ from those specified in the type
declarations. For example:

@example
Obj9 : Rec2 := (Rec => (Data1 => Constructor (15, 16),
                        others => <>),
                others => <>);
@end example

The above declaration uses an Ada 2005 limited aggregate to
initialize @code{Obj9}, and the C++ constructor that has two integer
arguments is invoked to initialize the @code{Data1} component instead
of the constructor specified in the declaration of type @code{Rec1}. In
Ada 2005 the box in the aggregate indicates that unspecified components
are initialized using the expression (if any) available in the component
declaration. That is, in this case discriminant @code{D} is initialized
to value @code{20}, @code{Value} is initialized to value 1000, and the
non-default C++ constructor that handles two integers takes care of
initializing component @code{Data2} with values @code{20,30}.

In Ada 2005 we can use the extended return statement to build the Ada
equivalent to C++ non-default constructors. For example:

@example
function Constructor (V : Integer) return Rec2 is
begin
   return Obj : Rec2 := (Rec => (Data1  => Constructor (V, 20),
                                 others => <>),
                         others => <>) do
      --  Further actions required for construction of
      --  objects of type Rec2
      ...
   end record;
end Constructor;
@end example

In this example the extended return statement construct is used to
build in place the returned object whose components are initialized
by means of a limited aggregate. Any further action associated with
the constructor can be placed inside the construct.

@node Interfacing with C++ at the Class Level,,Interfacing with C++ constructors,Building Mixed Ada and C++ Programs
@anchor{gnat_ugn/the_gnat_compilation_model interfacing-with-c-at-the-class-level}@anchor{c1}@anchor{gnat_ugn/the_gnat_compilation_model id69}@anchor{c2}
@subsubsection Interfacing with C++ at the Class Level


In this section we demonstrate the GNAT features for interfacing with
C++ by means of an example making use of Ada 2005 abstract interface
types. This example consists of a classification of animals; classes
have been used to model our main classification of animals, and
interfaces provide support for the management of secondary
classifications. We first demonstrate a case in which the types and
constructors are defined on the C++ side and imported from the Ada
side, and latter the reverse case.

The root of our derivation will be the @code{Animal} class, with a
single private attribute (the @code{Age} of the animal), a constructor,
and two public primitives to set and get the value of this attribute.

@example
class Animal @{
 public:
   virtual void Set_Age (int New_Age);
   virtual int Age ();
   Animal() @{Age_Count = 0;@};
 private:
   int Age_Count;
@};
@end example

Abstract interface types are defined in C++ by means of classes with pure
virtual functions and no data members. In our example we will use two
interfaces that provide support for the common management of @code{Carnivore}
and @code{Domestic} animals:

@example
class Carnivore @{
public:
   virtual int Number_Of_Teeth () = 0;
@};

class Domestic @{
public:
   virtual void Set_Owner (char* Name) = 0;
@};
@end example

Using these declarations, we can now say that a @code{Dog} is an animal that is
both Carnivore and Domestic, that is:

@example
class Dog : Animal, Carnivore, Domestic @{
 public:
   virtual int  Number_Of_Teeth ();
   virtual void Set_Owner (char* Name);

   Dog(); // Constructor
 private:
   int  Tooth_Count;
   char *Owner;
@};
@end example

In the following examples we will assume that the previous declarations are
located in a file named @code{animals.h}. The following package demonstrates
how to import these C++ declarations from the Ada side:

@example
with Interfaces.C.Strings; use Interfaces.C.Strings;
package Animals is
  type Carnivore is limited interface;
  pragma Convention (C_Plus_Plus, Carnivore);
  function Number_Of_Teeth (X : Carnivore)
     return Natural is abstract;

  type Domestic is limited interface;
  pragma Convention (C_Plus_Plus, Domestic);
  procedure Set_Owner
    (X    : in out Domestic;
     Name : Chars_Ptr) is abstract;

  type Animal is tagged limited record
    Age : Natural;
  end record;
  pragma Import (C_Plus_Plus, Animal);

  procedure Set_Age (X : in out Animal; Age : Integer);
  pragma Import (C_Plus_Plus, Set_Age);

  function Age (X : Animal) return Integer;
  pragma Import (C_Plus_Plus, Age);

  function New_Animal return Animal;
  pragma CPP_Constructor (New_Animal);
  pragma Import (CPP, New_Animal, "_ZN6AnimalC1Ev");

  type Dog is new Animal and Carnivore and Domestic with record
    Tooth_Count : Natural;
    Owner       : Chars_Ptr;
  end record;
  pragma Import (C_Plus_Plus, Dog);

  function Number_Of_Teeth (A : Dog) return Natural;
  pragma Import (C_Plus_Plus, Number_Of_Teeth);

  procedure Set_Owner (A : in out Dog; Name : Chars_Ptr);
  pragma Import (C_Plus_Plus, Set_Owner);

  function New_Dog return Dog;
  pragma CPP_Constructor (New_Dog);
  pragma Import (CPP, New_Dog, "_ZN3DogC2Ev");
end Animals;
@end example

Thanks to the compatibility between GNAT run-time structures and the C++ ABI,
interfacing with these C++ classes is easy. The only requirement is that all
the primitives and components must be declared exactly in the same order in
the two languages.

Regarding the abstract interfaces, we must indicate to the GNAT compiler by
means of a @code{pragma Convention (C_Plus_Plus)}, the convention used to pass
the arguments to the called primitives will be the same as for C++. For the
imported classes we use @code{pragma Import} with convention @code{C_Plus_Plus}
to indicate that they have been defined on the C++ side; this is required
because the dispatch table associated with these tagged types will be built
in the C++ side and therefore will not contain the predefined Ada primitives
which Ada would otherwise expect.

As the reader can see there is no need to indicate the C++ mangled names
associated with each subprogram because it is assumed that all the calls to
these primitives will be dispatching calls. The only exception is the
constructor, which must be registered with the compiler by means of
@code{pragma CPP_Constructor} and needs to provide its associated C++
mangled name because the Ada compiler generates direct calls to it.

With the above packages we can now declare objects of type Dog on the Ada side
and dispatch calls to the corresponding subprograms on the C++ side. We can
also extend the tagged type Dog with further fields and primitives, and
override some of its C++ primitives on the Ada side. For example, here we have
a type derivation defined on the Ada side that inherits all the dispatching
primitives of the ancestor from the C++ side.

@example
with Animals; use Animals;
package Vaccinated_Animals is
  type Vaccinated_Dog is new Dog with null record;
  function Vaccination_Expired (A : Vaccinated_Dog) return Boolean;
end Vaccinated_Animals;
@end example

It is important to note that, because of the ABI compatibility, the programmer
does not need to add any further information to indicate either the object
layout or the dispatch table entry associated with each dispatching operation.

Now let us define all the types and constructors on the Ada side and export
them to C++, using the same hierarchy of our previous example:

@example
with Interfaces.C.Strings;
use Interfaces.C.Strings;
package Animals is
  type Carnivore is limited interface;
  pragma Convention (C_Plus_Plus, Carnivore);
  function Number_Of_Teeth (X : Carnivore)
     return Natural is abstract;

  type Domestic is limited interface;
  pragma Convention (C_Plus_Plus, Domestic);
  procedure Set_Owner
    (X    : in out Domestic;
     Name : Chars_Ptr) is abstract;

  type Animal is tagged record
    Age : Natural;
  end record;
  pragma Convention (C_Plus_Plus, Animal);

  procedure Set_Age (X : in out Animal; Age : Integer);
  pragma Export (C_Plus_Plus, Set_Age);

  function Age (X : Animal) return Integer;
  pragma Export (C_Plus_Plus, Age);

  function New_Animal return Animal'Class;
  pragma Export (C_Plus_Plus, New_Animal);

  type Dog is new Animal and Carnivore and Domestic with record
    Tooth_Count : Natural;
    Owner       : String (1 .. 30);
  end record;
  pragma Convention (C_Plus_Plus, Dog);

  function Number_Of_Teeth (A : Dog) return Natural;
  pragma Export (C_Plus_Plus, Number_Of_Teeth);

  procedure Set_Owner (A : in out Dog; Name : Chars_Ptr);
  pragma Export (C_Plus_Plus, Set_Owner);

  function New_Dog return Dog'Class;
  pragma Export (C_Plus_Plus, New_Dog);
end Animals;
@end example

Compared with our previous example the only differences are the use of
@code{pragma Convention} (instead of @code{pragma Import}), and the use of
@code{pragma Export} to indicate to the GNAT compiler that the primitives will
be available to C++. Thanks to the ABI compatibility, on the C++ side there is
nothing else to be done; as explained above, the only requirement is that all
the primitives and components are declared in exactly the same order.

For completeness, let us see a brief C++ main program that uses the
declarations available in @code{animals.h} (presented in our first example) to
import and use the declarations from the Ada side, properly initializing and
finalizing the Ada run-time system along the way:

@example
#include "animals.h"
#include <iostream>
using namespace std;

void Check_Carnivore (Carnivore *obj) @{...@}
void Check_Domestic (Domestic *obj)   @{...@}
void Check_Animal (Animal *obj)       @{...@}
void Check_Dog (Dog *obj)             @{...@}

extern "C" @{
  void adainit (void);
  void adafinal (void);
  Dog* new_dog ();
@}

void test ()
@{
  Dog *obj = new_dog();  // Ada constructor
  Check_Carnivore (obj); // Check secondary DT
  Check_Domestic (obj);  // Check secondary DT
  Check_Animal (obj);    // Check primary DT
  Check_Dog (obj);       // Check primary DT
@}

int main ()
@{
  adainit ();  test();  adafinal ();
  return 0;
@}
@end example

@node Generating Ada Bindings for C and C++ headers,Generating C Headers for Ada Specifications,Building Mixed Ada and C++ Programs,Mixed Language Programming
@anchor{gnat_ugn/the_gnat_compilation_model id70}@anchor{c3}@anchor{gnat_ugn/the_gnat_compilation_model generating-ada-bindings-for-c-and-c-headers}@anchor{19}
@subsection Generating Ada Bindings for C and C++ headers


@geindex Binding generation (for C and C++ headers)

@geindex C headers (binding generation)

@geindex C++ headers (binding generation)

GNAT includes a binding generator for C and C++ headers which is
intended to do 95% of the tedious work of generating Ada specs from C
or C++ header files.

Note that this capability is not intended to generate 100% correct Ada specs,
and will is some cases require manual adjustments, although it can often
be used out of the box in practice.

Some of the known limitations include:


@itemize *

@item 
only very simple character constant macros are translated into Ada
constants. Function macros (macros with arguments) are partially translated
as comments, to be completed manually if needed.

@item 
some extensions (e.g. vector types) are not supported

@item 
pointers to pointers or complex structures are mapped to System.Address

@item 
identifiers with identical name (except casing) will generate compilation
errors (e.g. @code{shm_get} vs @code{SHM_GET}).
@end itemize

The code generated is using the Ada 2005 syntax, which makes it
easier to interface with other languages than previous versions of Ada.

@menu
* Running the Binding Generator:: 
* Generating Bindings for C++ Headers:: 
* Switches:: 

@end menu

@node Running the Binding Generator,Generating Bindings for C++ Headers,,Generating Ada Bindings for C and C++ headers
@anchor{gnat_ugn/the_gnat_compilation_model id71}@anchor{c4}@anchor{gnat_ugn/the_gnat_compilation_model running-the-binding-generator}@anchor{c5}
@subsubsection Running the Binding Generator


The binding generator is part of the @code{gcc} compiler and can be
invoked via the @code{-fdump-ada-spec} switch, which will generate Ada
spec files for the header files specified on the command line, and all
header files needed by these files transitively. For example:

@example
$ g++ -c -fdump-ada-spec -C /usr/include/time.h
$ gcc -c -gnat05 *.ads
@end example

will generate, under GNU/Linux, the following files: @code{time_h.ads},
@code{bits_time_h.ads}, @code{stddef_h.ads}, @code{bits_types_h.ads} which
correspond to the files @code{/usr/include/time.h},
@code{/usr/include/bits/time.h}, etc..., and will then compile these Ada specs
in Ada 2005 mode.

The @code{-C} switch tells @code{gcc} to extract comments from headers,
and will attempt to generate corresponding Ada comments.

If you want to generate a single Ada file and not the transitive closure, you
can use instead the @code{-fdump-ada-spec-slim} switch.

You can optionally specify a parent unit, of which all generated units will
be children, using @code{-fada-spec-parent=@emph{unit}}.

Note that we recommend when possible to use the @emph{g++} driver to
generate bindings, even for most C headers, since this will in general
generate better Ada specs. For generating bindings for C++ headers, it is
mandatory to use the @emph{g++} command, or @emph{gcc -x c++} which
is equivalent in this case. If @emph{g++} cannot work on your C headers
because of incompatibilities between C and C++, then you can fallback to
@code{gcc} instead.

For an example of better bindings generated from the C++ front-end,
the name of the parameters (when available) are actually ignored by the C
front-end. Consider the following C header:

@example
extern void foo (int variable);
@end example

with the C front-end, @code{variable} is ignored, and the above is handled as:

@example
extern void foo (int);
@end example

generating a generic:

@example
procedure foo (param1 : int);
@end example

with the C++ front-end, the name is available, and we generate:

@example
procedure foo (variable : int);
@end example

In some cases, the generated bindings will be more complete or more meaningful
when defining some macros, which you can do via the @code{-D} switch. This
is for example the case with @code{Xlib.h} under GNU/Linux:

@example
$ g++ -c -fdump-ada-spec -DXLIB_ILLEGAL_ACCESS -C /usr/include/X11/Xlib.h
@end example

The above will generate more complete bindings than a straight call without
the @code{-DXLIB_ILLEGAL_ACCESS} switch.

In other cases, it is not possible to parse a header file in a stand-alone
manner, because other include files need to be included first. In this
case, the solution is to create a small header file including the needed
@code{#include} and possible @code{#define} directives. For example, to
generate Ada bindings for @code{readline/readline.h}, you need to first
include @code{stdio.h}, so you can create a file with the following two
lines in e.g. @code{readline1.h}:

@example
#include <stdio.h>
#include <readline/readline.h>
@end example

and then generate Ada bindings from this file:

@example
$ g++ -c -fdump-ada-spec readline1.h
@end example

@node Generating Bindings for C++ Headers,Switches,Running the Binding Generator,Generating Ada Bindings for C and C++ headers
@anchor{gnat_ugn/the_gnat_compilation_model id72}@anchor{c6}@anchor{gnat_ugn/the_gnat_compilation_model generating-bindings-for-c-headers}@anchor{c7}
@subsubsection Generating Bindings for C++ Headers


Generating bindings for C++ headers is done using the same options, always
with the @emph{g++} compiler. Note that generating Ada spec from C++ headers is a
much more complex job and support for C++ headers is much more limited that
support for C headers. As a result, you will need to modify the resulting
bindings by hand more extensively when using C++ headers.

In this mode, C++ classes will be mapped to Ada tagged types, constructors
will be mapped using the @code{CPP_Constructor} pragma, and when possible,
multiple inheritance of abstract classes will be mapped to Ada interfaces
(see the @emph{Interfacing to C++} section in the @cite{GNAT Reference Manual}
for additional information on interfacing to C++).

For example, given the following C++ header file:

@example
class Carnivore @{
public:
   virtual int Number_Of_Teeth () = 0;
@};

class Domestic @{
public:
   virtual void Set_Owner (char* Name) = 0;
@};

class Animal @{
public:
  int Age_Count;
  virtual void Set_Age (int New_Age);
@};

class Dog : Animal, Carnivore, Domestic @{
 public:
  int  Tooth_Count;
  char *Owner;

  virtual int  Number_Of_Teeth ();
  virtual void Set_Owner (char* Name);

  Dog();
@};
@end example

The corresponding Ada code is generated:

@example
package Class_Carnivore is
  type Carnivore is limited interface;
  pragma Import (CPP, Carnivore);

  function Number_Of_Teeth (this : access Carnivore) return int is abstract;
end;
use Class_Carnivore;

package Class_Domestic is
  type Domestic is limited interface;
  pragma Import (CPP, Domestic);

  procedure Set_Owner
    (this : access Domestic;
     Name : Interfaces.C.Strings.chars_ptr) is abstract;
end;
use Class_Domestic;

package Class_Animal is
  type Animal is tagged limited record
    Age_Count : aliased int;
  end record;
  pragma Import (CPP, Animal);

  procedure Set_Age (this : access Animal; New_Age : int);
  pragma Import (CPP, Set_Age, "_ZN6Animal7Set_AgeEi");
end;
use Class_Animal;

package Class_Dog is
  type Dog is new Animal and Carnivore and Domestic with record
    Tooth_Count : aliased int;
    Owner : Interfaces.C.Strings.chars_ptr;
  end record;
  pragma Import (CPP, Dog);

  function Number_Of_Teeth (this : access Dog) return int;
  pragma Import (CPP, Number_Of_Teeth, "_ZN3Dog15Number_Of_TeethEv");

  procedure Set_Owner
    (this : access Dog; Name : Interfaces.C.Strings.chars_ptr);
  pragma Import (CPP, Set_Owner, "_ZN3Dog9Set_OwnerEPc");

  function New_Dog return Dog;
  pragma CPP_Constructor (New_Dog);
  pragma Import (CPP, New_Dog, "_ZN3DogC1Ev");
end;
use Class_Dog;
@end example

@node Switches,,Generating Bindings for C++ Headers,Generating Ada Bindings for C and C++ headers
@anchor{gnat_ugn/the_gnat_compilation_model switches}@anchor{c8}@anchor{gnat_ugn/the_gnat_compilation_model switches-for-ada-binding-generation}@anchor{c9}
@subsubsection Switches


@geindex -fdump-ada-spec (gcc)


@table @asis

@item @code{-fdump-ada-spec}

Generate Ada spec files for the given header files transitively (including
all header files that these headers depend upon).
@end table

@geindex -fdump-ada-spec-slim (gcc)


@table @asis

@item @code{-fdump-ada-spec-slim}

Generate Ada spec files for the header files specified on the command line
only.
@end table

@geindex -fada-spec-parent (gcc)


@table @asis

@item @code{-fada-spec-parent=@emph{unit}}

Specifies that all files generated by @code{-fdump-ada-spec} are
to be child units of the specified parent unit.
@end table

@geindex -C (gcc)


@table @asis

@item @code{-C}

Extract comments from headers and generate Ada comments in the Ada spec files.
@end table

@node Generating C Headers for Ada Specifications,,Generating Ada Bindings for C and C++ headers,Mixed Language Programming
@anchor{gnat_ugn/the_gnat_compilation_model generating-c-headers-for-ada-specifications}@anchor{ca}@anchor{gnat_ugn/the_gnat_compilation_model id73}@anchor{cb}
@subsection Generating C Headers for Ada Specifications


@geindex Binding generation (for Ada specs)

@geindex C headers (binding generation)

GNAT includes a C header generator for Ada specifications which supports
Ada types that have a direct mapping to C types. This includes in particular
support for:


@itemize *

@item 
Scalar types

@item 
Constrained arrays

@item 
Records (untagged)

@item 
Composition of the above types

@item 
Constant declarations

@item 
Object declarations

@item 
Subprogram declarations
@end itemize

@menu
* Running the C Header Generator:: 

@end menu

@node Running the C Header Generator,,,Generating C Headers for Ada Specifications
@anchor{gnat_ugn/the_gnat_compilation_model running-the-c-header-generator}@anchor{cc}
@subsubsection Running the C Header Generator


The C header generator is part of the GNAT compiler and can be invoked via
the @code{-gnatceg} combination of switches, which will generate a @code{.h}
file corresponding to the given input file (Ada spec or body). Note that
only spec files are processed in any case, so giving a spec or a body file
as input is equivalent. For example:

@example
$ gcc -c -gnatceg pack1.ads
@end example

will generate a self-contained file called @code{pack1.h} including
common definitions from the Ada Standard package, followed by the
definitions included in @code{pack1.ads}, as well as all the other units
withed by this file.

For instance, given the following Ada files:

@example
package Pack2 is
   type Int is range 1 .. 10;
end Pack2;
@end example

@example
with Pack2;

package Pack1 is
   type Rec is record
      Field1, Field2 : Pack2.Int;
   end record;

   Global : Rec := (1, 2);

   procedure Proc1 (R : Rec);
   procedure Proc2 (R : in out Rec);
end Pack1;
@end example

The above @code{gcc} command will generate the following @code{pack1.h} file:

@example
/* Standard definitions skipped */
#ifndef PACK2_ADS
#define PACK2_ADS
typedef short_short_integer pack2__TintB;
typedef pack2__TintB pack2__int;
#endif /* PACK2_ADS */

#ifndef PACK1_ADS
#define PACK1_ADS
typedef struct _pack1__rec @{
  pack2__int field1;
  pack2__int field2;
@} pack1__rec;
extern pack1__rec pack1__global;
extern void pack1__proc1(const pack1__rec r);
extern void pack1__proc2(pack1__rec *r);
#endif /* PACK1_ADS */
@end example

You can then @code{include} @code{pack1.h} from a C source file and use the types,
call subprograms, reference objects, and constants.

@node GNAT and Other Compilation Models,Using GNAT Files with External Tools,Mixed Language Programming,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model id74}@anchor{cd}@anchor{gnat_ugn/the_gnat_compilation_model gnat-and-other-compilation-models}@anchor{45}
@section GNAT and Other Compilation Models


This section compares the GNAT model with the approaches taken in
other environents, first the C/C++ model and then the mechanism that
has been used in other Ada systems, in particular those traditionally
used for Ada 83.

@menu
* Comparison between GNAT and C/C++ Compilation Models:: 
* Comparison between GNAT and Conventional Ada Library Models:: 

@end menu

@node Comparison between GNAT and C/C++ Compilation Models,Comparison between GNAT and Conventional Ada Library Models,,GNAT and Other Compilation Models
@anchor{gnat_ugn/the_gnat_compilation_model comparison-between-gnat-and-c-c-compilation-models}@anchor{ce}@anchor{gnat_ugn/the_gnat_compilation_model id75}@anchor{cf}
@subsection Comparison between GNAT and C/C++ Compilation Models


The GNAT model of compilation is close to the C and C++ models. You can
think of Ada specs as corresponding to header files in C. As in C, you
don't need to compile specs; they are compiled when they are used. The
Ada @emph{with} is similar in effect to the @code{#include} of a C
header.

One notable difference is that, in Ada, you may compile specs separately
to check them for semantic and syntactic accuracy. This is not always
possible with C headers because they are fragments of programs that have
less specific syntactic or semantic rules.

The other major difference is the requirement for running the binder,
which performs two important functions. First, it checks for
consistency. In C or C++, the only defense against assembling
inconsistent programs lies outside the compiler, in a makefile, for
example. The binder satisfies the Ada requirement that it be impossible
to construct an inconsistent program when the compiler is used in normal
mode.

@geindex Elaboration order control

The other important function of the binder is to deal with elaboration
issues. There are also elaboration issues in C++ that are handled
automatically. This automatic handling has the advantage of being
simpler to use, but the C++ programmer has no control over elaboration.
Where @code{gnatbind} might complain there was no valid order of
elaboration, a C++ compiler would simply construct a program that
malfunctioned at run time.

@node Comparison between GNAT and Conventional Ada Library Models,,Comparison between GNAT and C/C++ Compilation Models,GNAT and Other Compilation Models
@anchor{gnat_ugn/the_gnat_compilation_model comparison-between-gnat-and-conventional-ada-library-models}@anchor{d0}@anchor{gnat_ugn/the_gnat_compilation_model id76}@anchor{d1}
@subsection Comparison between GNAT and Conventional Ada Library Models


This section is intended for Ada programmers who have
used an Ada compiler implementing the traditional Ada library
model, as described in the Ada Reference Manual.

@geindex GNAT library

In GNAT, there is no 'library' in the normal sense. Instead, the set of
source files themselves acts as the library. Compiling Ada programs does
not generate any centralized information, but rather an object file and
a ALI file, which are of interest only to the binder and linker.
In a traditional system, the compiler reads information not only from
the source file being compiled, but also from the centralized library.
This means that the effect of a compilation depends on what has been
previously compiled. In particular:


@itemize *

@item 
When a unit is @emph{with}ed, the unit seen by the compiler corresponds
to the version of the unit most recently compiled into the library.

@item 
Inlining is effective only if the necessary body has already been
compiled into the library.

@item 
Compiling a unit may obsolete other units in the library.
@end itemize

In GNAT, compiling one unit never affects the compilation of any other
units because the compiler reads only source files. Only changes to source
files can affect the results of a compilation. In particular:


@itemize *

@item 
When a unit is @emph{with}ed, the unit seen by the compiler corresponds
to the source version of the unit that is currently accessible to the
compiler.

@geindex Inlining

@item 
Inlining requires the appropriate source files for the package or
subprogram bodies to be available to the compiler. Inlining is always
effective, independent of the order in which units are compiled.

@item 
Compiling a unit never affects any other compilations. The editing of
sources may cause previous compilations to be out of date if they
depended on the source file being modified.
@end itemize

The most important result of these differences is that order of compilation
is never significant in GNAT. There is no situation in which one is
required to do one compilation before another. What shows up as order of
compilation requirements in the traditional Ada library becomes, in
GNAT, simple source dependencies; in other words, there is only a set
of rules saying what source files must be present when a file is
compiled.

@node Using GNAT Files with External Tools,,GNAT and Other Compilation Models,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model using-gnat-files-with-external-tools}@anchor{1a}@anchor{gnat_ugn/the_gnat_compilation_model id77}@anchor{d2}
@section Using GNAT Files with External Tools


This section explains how files that are produced by GNAT may be
used with tools designed for other languages.

@menu
* Using Other Utility Programs with GNAT:: 
* The External Symbol Naming Scheme of GNAT:: 

@end menu

@node Using Other Utility Programs with GNAT,The External Symbol Naming Scheme of GNAT,,Using GNAT Files with External Tools
@anchor{gnat_ugn/the_gnat_compilation_model using-other-utility-programs-with-gnat}@anchor{d3}@anchor{gnat_ugn/the_gnat_compilation_model id78}@anchor{d4}
@subsection Using Other Utility Programs with GNAT


The object files generated by GNAT are in standard system format and in
particular the debugging information uses this format. This means
programs generated by GNAT can be used with existing utilities that
depend on these formats.

In general, any utility program that works with C will also often work with
Ada programs generated by GNAT. This includes software utilities such as
gprof (a profiling program), gdb (the FSF debugger), and utilities such
as Purify.

@node The External Symbol Naming Scheme of GNAT,,Using Other Utility Programs with GNAT,Using GNAT Files with External Tools
@anchor{gnat_ugn/the_gnat_compilation_model the-external-symbol-naming-scheme-of-gnat}@anchor{d5}@anchor{gnat_ugn/the_gnat_compilation_model id79}@anchor{d6}
@subsection The External Symbol Naming Scheme of GNAT


In order to interpret the output from GNAT, when using tools that are
originally intended for use with other languages, it is useful to
understand the conventions used to generate link names from the Ada
entity names.

All link names are in all lowercase letters. With the exception of library
procedure names, the mechanism used is simply to use the full expanded
Ada name with dots replaced by double underscores. For example, suppose
we have the following package spec:

@example
package QRS is
   MN : Integer;
end QRS;
@end example

@geindex pragma Export

The variable @code{MN} has a full expanded Ada name of @code{QRS.MN}, so
the corresponding link name is @code{qrs__mn}.
Of course if a @code{pragma Export} is used this may be overridden:

@example
package Exports is
   Var1 : Integer;
   pragma Export (Var1, C, External_Name => "var1_name");
   Var2 : Integer;
   pragma Export (Var2, C, Link_Name => "var2_link_name");
end Exports;
@end example

In this case, the link name for @code{Var1} is whatever link name the
C compiler would assign for the C function @code{var1_name}. This typically
would be either @code{var1_name} or @code{_var1_name}, depending on operating
system conventions, but other possibilities exist. The link name for
@code{Var2} is @code{var2_link_name}, and this is not operating system
dependent.

One exception occurs for library level procedures. A potential ambiguity
arises between the required name @code{_main} for the C main program,
and the name we would otherwise assign to an Ada library level procedure
called @code{Main} (which might well not be the main program).

To avoid this ambiguity, we attach the prefix @code{_ada_} to such
names. So if we have a library level procedure such as:

@example
procedure Hello (S : String);
@end example

the external name of this procedure will be @code{_ada_hello}.

@c -- Example: A |withing| unit has a |with| clause, it |withs| a |withed| unit

@node Building Executable Programs with GNAT,GNAT Utility Programs,The GNAT Compilation Model,Top
@anchor{gnat_ugn/building_executable_programs_with_gnat building-executable-programs-with-gnat}@anchor{a}@anchor{gnat_ugn/building_executable_programs_with_gnat doc}@anchor{d7}@anchor{gnat_ugn/building_executable_programs_with_gnat id1}@anchor{d8}
@chapter Building Executable Programs with GNAT


This chapter describes first the gnatmake tool
(@ref{1b,,Building with gnatmake}),
which automatically determines the set of sources
needed by an Ada compilation unit and executes the necessary
(re)compilations, binding and linking.
It also explains how to use each tool individually: the
compiler (gcc, see @ref{1c,,Compiling with gcc}),
binder (gnatbind, see @ref{1d,,Binding with gnatbind}),
and linker (gnatlink, see @ref{1e,,Linking with gnatlink})
to build executable programs.
Finally, this chapter provides examples of
how to make use of the general GNU make mechanism
in a GNAT context (see @ref{1f,,Using the GNU make Utility}).


@menu
* Building with gnatmake:: 
* Compiling with gcc:: 
* Compiler Switches:: 
* Linker Switches:: 
* Binding with gnatbind:: 
* Linking with gnatlink:: 
* Using the GNU make Utility:: 

@end menu

@node Building with gnatmake,Compiling with gcc,,Building Executable Programs with GNAT
@anchor{gnat_ugn/building_executable_programs_with_gnat the-gnat-make-program-gnatmake}@anchor{1b}@anchor{gnat_ugn/building_executable_programs_with_gnat building-with-gnatmake}@anchor{d9}
@section Building with @code{gnatmake}


@geindex gnatmake

A typical development cycle when working on an Ada program consists of
the following steps:


@enumerate 

@item 
Edit some sources to fix bugs;

@item 
Add enhancements;

@item 
Compile all sources affected;

@item 
Rebind and relink; and

@item 
Test.
@end enumerate

@geindex Dependency rules (compilation)

The third step in particular can be tricky, because not only do the modified
files have to be compiled, but any files depending on these files must also be
recompiled. The dependency rules in Ada can be quite complex, especially
in the presence of overloading, @code{use} clauses, generics and inlined
subprograms.

@code{gnatmake} automatically takes care of the third and fourth steps
of this process. It determines which sources need to be compiled,
compiles them, and binds and links the resulting object files.

Unlike some other Ada make programs, the dependencies are always
accurately recomputed from the new sources. The source based approach of
the GNAT compilation model makes this possible. This means that if
changes to the source program cause corresponding changes in
dependencies, they will always be tracked exactly correctly by
@code{gnatmake}.

Note that for advanced forms of project structure, we recommend creating
a project file as explained in the @emph{GNAT_Project_Manager} chapter in the
@emph{GPRbuild User's Guide}, and using the
@code{gprbuild} tool which supports building with project files and works similarly
to @code{gnatmake}.

@menu
* Running gnatmake:: 
* Switches for gnatmake:: 
* Mode Switches for gnatmake:: 
* Notes on the Command Line:: 
* How gnatmake Works:: 
* Examples of gnatmake Usage:: 

@end menu

@node Running gnatmake,Switches for gnatmake,,Building with gnatmake
@anchor{gnat_ugn/building_executable_programs_with_gnat running-gnatmake}@anchor{da}@anchor{gnat_ugn/building_executable_programs_with_gnat id2}@anchor{db}
@subsection Running @code{gnatmake}


The usual form of the @code{gnatmake} command is

@example
$ gnatmake [<switches>] <file_name> [<file_names>] [<mode_switches>]
@end example

The only required argument is one @code{file_name}, which specifies
a compilation unit that is a main program. Several @code{file_names} can be
specified: this will result in several executables being built.
If @code{switches} are present, they can be placed before the first
@code{file_name}, between @code{file_names} or after the last @code{file_name}.
If @code{mode_switches} are present, they must always be placed after
the last @code{file_name} and all @code{switches}.

If you are using standard file extensions (@code{.adb} and
@code{.ads}), then the
extension may be omitted from the @code{file_name} arguments. However, if
you are using non-standard extensions, then it is required that the
extension be given. A relative or absolute directory path can be
specified in a @code{file_name}, in which case, the input source file will
be searched for in the specified directory only. Otherwise, the input
source file will first be searched in the directory where
@code{gnatmake} was invoked and if it is not found, it will be search on
the source path of the compiler as described in
@ref{89,,Search Paths and the Run-Time Library (RTL)}.

All @code{gnatmake} output (except when you specify @code{-M}) is sent to
@code{stderr}. The output produced by the
@code{-M} switch is sent to @code{stdout}.

@node Switches for gnatmake,Mode Switches for gnatmake,Running gnatmake,Building with gnatmake
@anchor{gnat_ugn/building_executable_programs_with_gnat switches-for-gnatmake}@anchor{dc}@anchor{gnat_ugn/building_executable_programs_with_gnat id3}@anchor{dd}
@subsection Switches for @code{gnatmake}


You may specify any of the following switches to @code{gnatmake}:

@geindex --version (gnatmake)


@table @asis

@item @code{--version}

Display Copyright and version, then exit disregarding all other options.
@end table

@geindex --help (gnatmake)


@table @asis

@item @code{--help}

If @code{--version} was not used, display usage, then exit disregarding
all other options.
@end table

@geindex --GCC=compiler_name (gnatmake)


@table @asis

@item @code{--GCC=@emph{compiler_name}}

Program used for compiling. The default is @code{gcc}. You need to use
quotes around @code{compiler_name} if @code{compiler_name} contains
spaces or other separator characters.
As an example @code{--GCC="foo -x  -y"}
will instruct @code{gnatmake} to use @code{foo -x -y} as your
compiler. A limitation of this syntax is that the name and path name of
the executable itself must not include any embedded spaces. Note that
switch @code{-c} is always inserted after your command name. Thus in the
above example the compiler command that will be used by @code{gnatmake}
will be @code{foo -c -x -y}. If several @code{--GCC=compiler_name} are
used, only the last @code{compiler_name} is taken into account. However,
all the additional switches are also taken into account. Thus,
@code{--GCC="foo -x -y" --GCC="bar -z -t"} is equivalent to
@code{--GCC="bar -x -y -z -t"}.
@end table

@geindex --GNATBIND=binder_name (gnatmake)


@table @asis

@item @code{--GNATBIND=@emph{binder_name}}

Program used for binding. The default is @code{gnatbind}. You need to
use quotes around @code{binder_name} if @code{binder_name} contains spaces
or other separator characters.
As an example @code{--GNATBIND="bar -x  -y"}
will instruct @code{gnatmake} to use @code{bar -x -y} as your
binder. Binder switches that are normally appended by @code{gnatmake}
to @code{gnatbind} are now appended to the end of @code{bar -x -y}.
A limitation of this syntax is that the name and path name of the executable
itself must not include any embedded spaces.
@end table

@geindex --GNATLINK=linker_name (gnatmake)


@table @asis

@item @code{--GNATLINK=@emph{linker_name}}

Program used for linking. The default is @code{gnatlink}. You need to
use quotes around @code{linker_name} if @code{linker_name} contains spaces
or other separator characters.
As an example @code{--GNATLINK="lan -x  -y"}
will instruct @code{gnatmake} to use @code{lan -x -y} as your
linker. Linker switches that are normally appended by @code{gnatmake} to
@code{gnatlink} are now appended to the end of @code{lan -x -y}.
A limitation of this syntax is that the name and path name of the executable
itself must not include any embedded spaces.

@item @code{--create-map-file}

When linking an executable, create a map file. The name of the map file
has the same name as the executable with extension ".map".

@item @code{--create-map-file=@emph{mapfile}}

When linking an executable, create a map file with the specified name.
@end table

@geindex --create-missing-dirs (gnatmake)


@table @asis

@item @code{--create-missing-dirs}

When using project files (@code{-P@emph{project}}), automatically create
missing object directories, library directories and exec
directories.

@item @code{--single-compile-per-obj-dir}

Disallow simultaneous compilations in the same object directory when
project files are used.

@item @code{--subdirs=@emph{subdir}}

Actual object directory of each project file is the subdirectory subdir of the
object directory specified or defaulted in the project file.

@item @code{--unchecked-shared-lib-imports}

By default, shared library projects are not allowed to import static library
projects. When this switch is used on the command line, this restriction is
relaxed.

@item @code{--source-info=@emph{source info file}}

Specify a source info file. This switch is active only when project files
are used. If the source info file is specified as a relative path, then it is
relative to the object directory of the main project. If the source info file
does not exist, then after the Project Manager has successfully parsed and
processed the project files and found the sources, it creates the source info
file. If the source info file already exists and can be read successfully,
then the Project Manager will get all the needed information about the sources
from the source info file and will not look for them. This reduces the time
to process the project files, especially when looking for sources that take a
long time. If the source info file exists but cannot be parsed successfully,
the Project Manager will attempt to recreate it. If the Project Manager fails
to create the source info file, a message is issued, but gnatmake does not
fail. @code{gnatmake} "trusts" the source info file. This means that
if the source files have changed (addition, deletion, moving to a different
source directory), then the source info file need to be deleted and recreated.
@end table

@geindex -a (gnatmake)


@table @asis

@item @code{-a}

Consider all files in the make process, even the GNAT internal system
files (for example, the predefined Ada library files), as well as any
locked files. Locked files are files whose ALI file is write-protected.
By default,
@code{gnatmake} does not check these files,
because the assumption is that the GNAT internal files are properly up
to date, and also that any write protected ALI files have been properly
installed. Note that if there is an installation problem, such that one
of these files is not up to date, it will be properly caught by the
binder.
You may have to specify this switch if you are working on GNAT
itself. The switch @code{-a} is also useful
in conjunction with @code{-f}
if you need to recompile an entire application,
including run-time files, using special configuration pragmas,
such as a @code{Normalize_Scalars} pragma.

By default
@code{gnatmake -a} compiles all GNAT
internal files with
@code{gcc -c -gnatpg} rather than @code{gcc -c}.
@end table

@geindex -b (gnatmake)


@table @asis

@item @code{-b}

Bind only. Can be combined with @code{-c} to do
compilation and binding, but no link.
Can be combined with @code{-l}
to do binding and linking. When not combined with
@code{-c}
all the units in the closure of the main program must have been previously
compiled and must be up to date. The root unit specified by @code{file_name}
may be given without extension, with the source extension or, if no GNAT
Project File is specified, with the ALI file extension.
@end table

@geindex -c (gnatmake)


@table @asis

@item @code{-c}

Compile only. Do not perform binding, except when @code{-b}
is also specified. Do not perform linking, except if both
@code{-b} and
@code{-l} are also specified.
If the root unit specified by @code{file_name} is not a main unit, this is the
default. Otherwise @code{gnatmake} will attempt binding and linking
unless all objects are up to date and the executable is more recent than
the objects.
@end table

@geindex -C (gnatmake)


@table @asis

@item @code{-C}

Use a temporary mapping file. A mapping file is a way to communicate
to the compiler two mappings: from unit names to file names (without
any directory information) and from file names to path names (with
full directory information). A mapping file can make the compiler's
file searches faster, especially if there are many source directories,
or the sources are read over a slow network connection. If
@code{-P} is used, a mapping file is always used, so
@code{-C} is unnecessary; in this case the mapping file
is initially populated based on the project file. If
@code{-C} is used without
@code{-P},
the mapping file is initially empty. Each invocation of the compiler
will add any newly accessed sources to the mapping file.
@end table

@geindex -C= (gnatmake)


@table @asis

@item @code{-C=@emph{file}}

Use a specific mapping file. The file, specified as a path name (absolute or
relative) by this switch, should already exist, otherwise the switch is
ineffective. The specified mapping file will be communicated to the compiler.
This switch is not compatible with a project file
(-P`file`) or with multiple compiling processes
(-jnnn, when nnn is greater than 1).
@end table

@geindex -d (gnatmake)


@table @asis

@item @code{-d}

Display progress for each source, up to date or not, as a single line:

@example
completed x out of y (zz%)
@end example

If the file needs to be compiled this is displayed after the invocation of
the compiler. These lines are displayed even in quiet output mode.
@end table

@geindex -D (gnatmake)


@table @asis

@item @code{-D @emph{dir}}

Put all object files and ALI file in directory @code{dir}.
If the @code{-D} switch is not used, all object files
and ALI files go in the current working directory.

This switch cannot be used when using a project file.
@end table

@geindex -eI (gnatmake)


@table @asis

@item @code{-eI@emph{nnn}}

Indicates that the main source is a multi-unit source and the rank of the unit
in the source file is nnn. nnn needs to be a positive number and a valid
index in the source. This switch cannot be used when @code{gnatmake} is
invoked for several mains.
@end table

@geindex -eL (gnatmake)

@geindex symbolic links


@table @asis

@item @code{-eL}

Follow all symbolic links when processing project files.
This should be used if your project uses symbolic links for files or
directories, but is not needed in other cases.

@geindex naming scheme

This also assumes that no directory matches the naming scheme for files (for
instance that you do not have a directory called "sources.ads" when using the
default GNAT naming scheme).

When you do not have to use this switch (i.e., by default), gnatmake is able to
save a lot of system calls (several per source file and object file), which
can result in a significant speed up to load and manipulate a project file,
especially when using source files from a remote system.
@end table

@geindex -eS (gnatmake)


@table @asis

@item @code{-eS}

Output the commands for the compiler, the binder and the linker
on standard output,
instead of standard error.
@end table

@geindex -f (gnatmake)


@table @asis

@item @code{-f}

Force recompilations. Recompile all sources, even though some object
files may be up to date, but don't recompile predefined or GNAT internal
files or locked files (files with a write-protected ALI file),
unless the @code{-a} switch is also specified.
@end table

@geindex -F (gnatmake)


@table @asis

@item @code{-F}

When using project files, if some errors or warnings are detected during
parsing and verbose mode is not in effect (no use of switch
-v), then error lines start with the full path name of the project
file, rather than its simple file name.
@end table

@geindex -g (gnatmake)


@table @asis

@item @code{-g}

Enable debugging. This switch is simply passed to the compiler and to the
linker.
@end table

@geindex -i (gnatmake)


@table @asis

@item @code{-i}

In normal mode, @code{gnatmake} compiles all object files and ALI files
into the current directory. If the @code{-i} switch is used,
then instead object files and ALI files that already exist are overwritten
in place. This means that once a large project is organized into separate
directories in the desired manner, then @code{gnatmake} will automatically
maintain and update this organization. If no ALI files are found on the
Ada object path (see @ref{89,,Search Paths and the Run-Time Library (RTL)}),
the new object and ALI files are created in the
directory containing the source being compiled. If another organization
is desired, where objects and sources are kept in different directories,
a useful technique is to create dummy ALI files in the desired directories.
When detecting such a dummy file, @code{gnatmake} will be forced to
recompile the corresponding source file, and it will be put the resulting
object and ALI files in the directory where it found the dummy file.
@end table

@geindex -j (gnatmake)

@geindex Parallel make


@table @asis

@item @code{-j@emph{n}}

Use @code{n} processes to carry out the (re)compilations. On a multiprocessor
machine compilations will occur in parallel. If @code{n} is 0, then the
maximum number of parallel compilations is the number of core processors
on the platform. In the event of compilation errors, messages from various
compilations might get interspersed (but @code{gnatmake} will give you the
full ordered list of failing compiles at the end). If this is problematic,
rerun the make process with n set to 1 to get a clean list of messages.
@end table

@geindex -k (gnatmake)


@table @asis

@item @code{-k}

Keep going. Continue as much as possible after a compilation error. To
ease the programmer's task in case of compilation errors, the list of
sources for which the compile fails is given when @code{gnatmake}
terminates.

If @code{gnatmake} is invoked with several @code{file_names} and with this
switch, if there are compilation errors when building an executable,
@code{gnatmake} will not attempt to build the following executables.
@end table

@geindex -l (gnatmake)


@table @asis

@item @code{-l}

Link only. Can be combined with @code{-b} to binding
and linking. Linking will not be performed if combined with
@code{-c}
but not with @code{-b}.
When not combined with @code{-b}
all the units in the closure of the main program must have been previously
compiled and must be up to date, and the main program needs to have been bound.
The root unit specified by @code{file_name}
may be given without extension, with the source extension or, if no GNAT
Project File is specified, with the ALI file extension.
@end table

@geindex -m (gnatmake)


@table @asis

@item @code{-m}

Specify that the minimum necessary amount of recompilations
be performed. In this mode @code{gnatmake} ignores time
stamp differences when the only
modifications to a source file consist in adding/removing comments,
empty lines, spaces or tabs. This means that if you have changed the
comments in a source file or have simply reformatted it, using this
switch will tell @code{gnatmake} not to recompile files that depend on it
(provided other sources on which these files depend have undergone no
semantic modifications). Note that the debugging information may be
out of date with respect to the sources if the @code{-m} switch causes
a compilation to be switched, so the use of this switch represents a
trade-off between compilation time and accurate debugging information.
@end table

@geindex Dependencies
@geindex producing list

@geindex -M (gnatmake)


@table @asis

@item @code{-M}

Check if all objects are up to date. If they are, output the object
dependences to @code{stdout} in a form that can be directly exploited in
a @code{Makefile}. By default, each source file is prefixed with its
(relative or absolute) directory name. This name is whatever you
specified in the various @code{-aI}
and @code{-I} switches. If you use
@code{gnatmake -M}  @code{-q}
(see below), only the source file names,
without relative paths, are output. If you just specify the  @code{-M}
switch, dependencies of the GNAT internal system files are omitted. This
is typically what you want. If you also specify
the @code{-a} switch,
dependencies of the GNAT internal files are also listed. Note that
dependencies of the objects in external Ada libraries (see
switch  @code{-aL@emph{dir}} in the following list)
are never reported.
@end table

@geindex -n (gnatmake)


@table @asis

@item @code{-n}

Don't compile, bind, or link. Checks if all objects are up to date.
If they are not, the full name of the first file that needs to be
recompiled is printed.
Repeated use of this option, followed by compiling the indicated source
file, will eventually result in recompiling all required units.
@end table

@geindex -o (gnatmake)


@table @asis

@item @code{-o @emph{exec_name}}

Output executable name. The name of the final executable program will be
@code{exec_name}. If the @code{-o} switch is omitted the default
name for the executable will be the name of the input file in appropriate form
for an executable file on the host system.

This switch cannot be used when invoking @code{gnatmake} with several
@code{file_names}.
@end table

@geindex -p (gnatmake)


@table @asis

@item @code{-p}

Same as @code{--create-missing-dirs}
@end table

@geindex -P (gnatmake)


@table @asis

@item @code{-P@emph{project}}

Use project file @code{project}. Only one such switch can be used.
@end table

@c -- Comment:
@c :ref:`gnatmake_and_Project_Files`.

@geindex -q (gnatmake)


@table @asis

@item @code{-q}

Quiet. When this flag is not set, the commands carried out by
@code{gnatmake} are displayed.
@end table

@geindex -s (gnatmake)


@table @asis

@item @code{-s}

Recompile if compiler switches have changed since last compilation.
All compiler switches but -I and -o are taken into account in the
following way:
orders between different 'first letter' switches are ignored, but
orders between same switches are taken into account. For example,
@code{-O -O2} is different than @code{-O2 -O}, but @code{-g -O}
is equivalent to @code{-O -g}.

This switch is recommended when Integrated Preprocessing is used.
@end table

@geindex -u (gnatmake)


@table @asis

@item @code{-u}

Unique. Recompile at most the main files. It implies -c. Combined with
-f, it is equivalent to calling the compiler directly. Note that using
-u with a project file and no main has a special meaning.
@end table

@c --Comment
@c (See :ref:`Project_Files_and_Main_Subprograms`.)

@geindex -U (gnatmake)


@table @asis

@item @code{-U}

When used without a project file or with one or several mains on the command
line, is equivalent to -u. When used with a project file and no main
on the command line, all sources of all project files are checked and compiled
if not up to date, and libraries are rebuilt, if necessary.
@end table

@geindex -v (gnatmake)


@table @asis

@item @code{-v}

Verbose. Display the reason for all recompilations @code{gnatmake}
decides are necessary, with the highest verbosity level.
@end table

@geindex -vl (gnatmake)


@table @asis

@item @code{-vl}

Verbosity level Low. Display fewer lines than in verbosity Medium.
@end table

@geindex -vm (gnatmake)


@table @asis

@item @code{-vm}

Verbosity level Medium. Potentially display fewer lines than in verbosity High.
@end table

@geindex -vm (gnatmake)


@table @asis

@item @code{-vh}

Verbosity level High. Equivalent to -v.

@item @code{-vP@emph{x}}

Indicate the verbosity of the parsing of GNAT project files.
See @ref{de,,Switches Related to Project Files}.
@end table

@geindex -x (gnatmake)


@table @asis

@item @code{-x}

Indicate that sources that are not part of any Project File may be compiled.
Normally, when using Project Files, only sources that are part of a Project
File may be compile. When this switch is used, a source outside of all Project
Files may be compiled. The ALI file and the object file will be put in the
object directory of the main Project. The compilation switches used will only
be those specified on the command line. Even when
@code{-x} is used, mains specified on the
command line need to be sources of a project file.

@item @code{-X@emph{name}=@emph{value}}

Indicate that external variable @code{name} has the value @code{value}.
The Project Manager will use this value for occurrences of
@code{external(name)} when parsing the project file.
@ref{de,,Switches Related to Project Files}.
@end table

@geindex -z (gnatmake)


@table @asis

@item @code{-z}

No main subprogram. Bind and link the program even if the unit name
given on the command line is a package name. The resulting executable
will execute the elaboration routines of the package and its closure,
then the finalization routines.
@end table

@subsubheading GCC switches


Any uppercase or multi-character switch that is not a @code{gnatmake} switch
is passed to @code{gcc} (e.g., @code{-O}, @code{-gnato,} etc.)

@subsubheading Source and library search path switches


@geindex -aI (gnatmake)


@table @asis

@item @code{-aI@emph{dir}}

When looking for source files also look in directory @code{dir}.
The order in which source files search is undertaken is
described in @ref{89,,Search Paths and the Run-Time Library (RTL)}.
@end table

@geindex -aL (gnatmake)


@table @asis

@item @code{-aL@emph{dir}}

Consider @code{dir} as being an externally provided Ada library.
Instructs @code{gnatmake} to skip compilation units whose @code{.ALI}
files have been located in directory @code{dir}. This allows you to have
missing bodies for the units in @code{dir} and to ignore out of date bodies
for the same units. You still need to specify
the location of the specs for these units by using the switches
@code{-aI@emph{dir}}  or @code{-I@emph{dir}}.
Note: this switch is provided for compatibility with previous versions
of @code{gnatmake}. The easier method of causing standard libraries
to be excluded from consideration is to write-protect the corresponding
ALI files.
@end table

@geindex -aO (gnatmake)


@table @asis

@item @code{-aO@emph{dir}}

When searching for library and object files, look in directory
@code{dir}. The order in which library files are searched is described in
@ref{8c,,Search Paths for gnatbind}.
@end table

@geindex Search paths
@geindex for gnatmake

@geindex -A (gnatmake)


@table @asis

@item @code{-A@emph{dir}}

Equivalent to @code{-aL@emph{dir}} @code{-aI@emph{dir}}.

@geindex -I (gnatmake)

@item @code{-I@emph{dir}}

Equivalent to @code{-aO@emph{dir} -aI@emph{dir}}.
@end table

@geindex -I- (gnatmake)

@geindex Source files
@geindex suppressing search


@table @asis

@item @code{-I-}

Do not look for source files in the directory containing the source
file named in the command line.
Do not look for ALI or object files in the directory
where @code{gnatmake} was invoked.
@end table

@geindex -L (gnatmake)

@geindex Linker libraries


@table @asis

@item @code{-L@emph{dir}}

Add directory @code{dir} to the list of directories in which the linker
will search for libraries. This is equivalent to
@code{-largs} @code{-L@emph{dir}}.
Furthermore, under Windows, the sources pointed to by the libraries path
set in the registry are not searched for.
@end table

@geindex -nostdinc (gnatmake)


@table @asis

@item @code{-nostdinc}

Do not look for source files in the system default directory.
@end table

@geindex -nostdlib (gnatmake)


@table @asis

@item @code{-nostdlib}

Do not look for library files in the system default directory.
@end table

@geindex --RTS (gnatmake)


@table @asis

@item @code{--RTS=@emph{rts-path}}

Specifies the default location of the run-time library. GNAT looks for the
run-time
in the following directories, and stops as soon as a valid run-time is found
(@code{adainclude} or @code{ada_source_path}, and @code{adalib} or
@code{ada_object_path} present):


@itemize *

@item 
@emph{<current directory>/$rts_path}

@item 
@emph{<default-search-dir>/$rts_path}

@item 
@emph{<default-search-dir>/rts-$rts_path}

@item 
The selected path is handled like a normal RTS path.
@end itemize
@end table

@node Mode Switches for gnatmake,Notes on the Command Line,Switches for gnatmake,Building with gnatmake
@anchor{gnat_ugn/building_executable_programs_with_gnat id4}@anchor{df}@anchor{gnat_ugn/building_executable_programs_with_gnat mode-switches-for-gnatmake}@anchor{e0}
@subsection Mode Switches for @code{gnatmake}


The mode switches (referred to as @code{mode_switches}) allow the
inclusion of switches that are to be passed to the compiler itself, the
binder or the linker. The effect of a mode switch is to cause all
subsequent switches up to the end of the switch list, or up to the next
mode switch, to be interpreted as switches to be passed on to the
designated component of GNAT.

@geindex -cargs (gnatmake)


@table @asis

@item @code{-cargs @emph{switches}}

Compiler switches. Here @code{switches} is a list of switches
that are valid switches for @code{gcc}. They will be passed on to
all compile steps performed by @code{gnatmake}.
@end table

@geindex -bargs (gnatmake)


@table @asis

@item @code{-bargs @emph{switches}}

Binder switches. Here @code{switches} is a list of switches
that are valid switches for @code{gnatbind}. They will be passed on to
all bind steps performed by @code{gnatmake}.
@end table

@geindex -largs (gnatmake)


@table @asis

@item @code{-largs @emph{switches}}

Linker switches. Here @code{switches} is a list of switches
that are valid switches for @code{gnatlink}. They will be passed on to
all link steps performed by @code{gnatmake}.
@end table

@geindex -margs (gnatmake)


@table @asis

@item @code{-margs @emph{switches}}

Make switches. The switches are directly interpreted by @code{gnatmake},
regardless of any previous occurrence of @code{-cargs}, @code{-bargs}
or @code{-largs}.
@end table

@node Notes on the Command Line,How gnatmake Works,Mode Switches for gnatmake,Building with gnatmake
@anchor{gnat_ugn/building_executable_programs_with_gnat id5}@anchor{e1}@anchor{gnat_ugn/building_executable_programs_with_gnat notes-on-the-command-line}@anchor{e2}
@subsection Notes on the Command Line


This section contains some additional useful notes on the operation
of the @code{gnatmake} command.

@geindex Recompilation (by gnatmake)


@itemize *

@item 
If @code{gnatmake} finds no ALI files, it recompiles the main program
and all other units required by the main program.
This means that @code{gnatmake}
can be used for the initial compile, as well as during subsequent steps of
the development cycle.

@item 
If you enter @code{gnatmake foo.adb}, where @code{foo}
is a subunit or body of a generic unit, @code{gnatmake} recompiles
@code{foo.adb} (because it finds no ALI) and stops, issuing a
warning.

@item 
In @code{gnatmake} the switch @code{-I}
is used to specify both source and
library file paths. Use @code{-aI}
instead if you just want to specify
source paths only and @code{-aO}
if you want to specify library paths
only.

@item 
@code{gnatmake} will ignore any files whose ALI file is write-protected.
This may conveniently be used to exclude standard libraries from
consideration and in particular it means that the use of the
@code{-f} switch will not recompile these files
unless @code{-a} is also specified.

@item 
@code{gnatmake} has been designed to make the use of Ada libraries
particularly convenient. Assume you have an Ada library organized
as follows: @emph{obj-dir} contains the objects and ALI files for
of your Ada compilation units,
whereas @emph{include-dir} contains the
specs of these units, but no bodies. Then to compile a unit
stored in @code{main.adb}, which uses this Ada library you would just type:

@example
$ gnatmake -aI`include-dir`  -aL`obj-dir`  main
@end example

@item 
Using @code{gnatmake} along with the @code{-m (minimal recompilation)}
switch provides a mechanism for avoiding unnecessary recompilations. Using
this switch,
you can update the comments/format of your
source files without having to recompile everything. Note, however, that
adding or deleting lines in a source files may render its debugging
info obsolete. If the file in question is a spec, the impact is rather
limited, as that debugging info will only be useful during the
elaboration phase of your program. For bodies the impact can be more
significant. In all events, your debugger will warn you if a source file
is more recent than the corresponding object, and alert you to the fact
that the debugging information may be out of date.
@end itemize

@node How gnatmake Works,Examples of gnatmake Usage,Notes on the Command Line,Building with gnatmake
@anchor{gnat_ugn/building_executable_programs_with_gnat id6}@anchor{e3}@anchor{gnat_ugn/building_executable_programs_with_gnat how-gnatmake-works}@anchor{e4}
@subsection How @code{gnatmake} Works


Generally @code{gnatmake} automatically performs all necessary
recompilations and you don't need to worry about how it works. However,
it may be useful to have some basic understanding of the @code{gnatmake}
approach and in particular to understand how it uses the results of
previous compilations without incorrectly depending on them.

First a definition: an object file is considered @emph{up to date} if the
corresponding ALI file exists and if all the source files listed in the
dependency section of this ALI file have time stamps matching those in
the ALI file. This means that neither the source file itself nor any
files that it depends on have been modified, and hence there is no need
to recompile this file.

@code{gnatmake} works by first checking if the specified main unit is up
to date. If so, no compilations are required for the main unit. If not,
@code{gnatmake} compiles the main program to build a new ALI file that
reflects the latest sources. Then the ALI file of the main unit is
examined to find all the source files on which the main program depends,
and @code{gnatmake} recursively applies the above procedure on all these
files.

This process ensures that @code{gnatmake} only trusts the dependencies
in an existing ALI file if they are known to be correct. Otherwise it
always recompiles to determine a new, guaranteed accurate set of
dependencies. As a result the program is compiled 'upside down' from what may
be more familiar as the required order of compilation in some other Ada
systems. In particular, clients are compiled before the units on which
they depend. The ability of GNAT to compile in any order is critical in
allowing an order of compilation to be chosen that guarantees that
@code{gnatmake} will recompute a correct set of new dependencies if
necessary.

When invoking @code{gnatmake} with several @code{file_names}, if a unit is
imported by several of the executables, it will be recompiled at most once.

Note: when using non-standard naming conventions
(@ref{35,,Using Other File Names}), changing through a configuration pragmas
file the version of a source and invoking @code{gnatmake} to recompile may
have no effect, if the previous version of the source is still accessible
by @code{gnatmake}. It may be necessary to use the switch
-f.

@node Examples of gnatmake Usage,,How gnatmake Works,Building with gnatmake
@anchor{gnat_ugn/building_executable_programs_with_gnat examples-of-gnatmake-usage}@anchor{e5}@anchor{gnat_ugn/building_executable_programs_with_gnat id7}@anchor{e6}
@subsection Examples of @code{gnatmake} Usage



@table @asis

@item @emph{gnatmake hello.adb}

Compile all files necessary to bind and link the main program
@code{hello.adb} (containing unit @code{Hello}) and bind and link the
resulting object files to generate an executable file @code{hello}.

@item @emph{gnatmake main1 main2 main3}

Compile all files necessary to bind and link the main programs
@code{main1.adb} (containing unit @code{Main1}), @code{main2.adb}
(containing unit @code{Main2}) and @code{main3.adb}
(containing unit @code{Main3}) and bind and link the resulting object files
to generate three executable files @code{main1},
@code{main2}  and @code{main3}.

@item @emph{gnatmake -q Main_Unit -cargs -O2 -bargs -l}

Compile all files necessary to bind and link the main program unit
@code{Main_Unit} (from file @code{main_unit.adb}). All compilations will
be done with optimization level 2 and the order of elaboration will be
listed by the binder. @code{gnatmake} will operate in quiet mode, not
displaying commands it is executing.
@end table

@node Compiling with gcc,Compiler Switches,Building with gnatmake,Building Executable Programs with GNAT
@anchor{gnat_ugn/building_executable_programs_with_gnat compiling-with-gcc}@anchor{1c}@anchor{gnat_ugn/building_executable_programs_with_gnat id8}@anchor{e7}
@section Compiling with @code{gcc}


This section discusses how to compile Ada programs using the @code{gcc}
command. It also describes the set of switches
that can be used to control the behavior of the compiler.

@menu
* Compiling Programs:: 
* Search Paths and the Run-Time Library (RTL): Search Paths and the Run-Time Library RTL. 
* Order of Compilation Issues:: 
* Examples:: 

@end menu

@node Compiling Programs,Search Paths and the Run-Time Library RTL,,Compiling with gcc
@anchor{gnat_ugn/building_executable_programs_with_gnat compiling-programs}@anchor{e8}@anchor{gnat_ugn/building_executable_programs_with_gnat id9}@anchor{e9}
@subsection Compiling Programs


The first step in creating an executable program is to compile the units
of the program using the @code{gcc} command. You must compile the
following files:


@itemize *

@item 
the body file (@code{.adb}) for a library level subprogram or generic
subprogram

@item 
the spec file (@code{.ads}) for a library level package or generic
package that has no body

@item 
the body file (@code{.adb}) for a library level package
or generic package that has a body
@end itemize

You need @emph{not} compile the following files


@itemize *

@item 
the spec of a library unit which has a body

@item 
subunits
@end itemize

because they are compiled as part of compiling related units. GNAT
package specs
when the corresponding body is compiled, and subunits when the parent is
compiled.

@geindex cannot generate code

If you attempt to compile any of these files, you will get one of the
following error messages (where @code{fff} is the name of the file you
compiled):

@quotation

@example
cannot generate code for file `@w{`}fff`@w{`} (package spec)
to check package spec, use -gnatc

cannot generate code for file `@w{`}fff`@w{`} (missing subunits)
to check parent unit, use -gnatc

cannot generate code for file `@w{`}fff`@w{`} (subprogram spec)
to check subprogram spec, use -gnatc

cannot generate code for file `@w{`}fff`@w{`} (subunit)
to check subunit, use -gnatc
@end example
@end quotation

As indicated by the above error messages, if you want to submit
one of these files to the compiler to check for correct semantics
without generating code, then use the @code{-gnatc} switch.

The basic command for compiling a file containing an Ada unit is:

@example
$ gcc -c [switches] <file name>
@end example

where @code{file name} is the name of the Ada file (usually
having an extension @code{.ads} for a spec or @code{.adb} for a body).
You specify the
@code{-c} switch to tell @code{gcc} to compile, but not link, the file.
The result of a successful compilation is an object file, which has the
same name as the source file but an extension of @code{.o} and an Ada
Library Information (ALI) file, which also has the same name as the
source file, but with @code{.ali} as the extension. GNAT creates these
two output files in the current directory, but you may specify a source
file in any directory using an absolute or relative path specification
containing the directory information.

TESTING: the @code{--foobar@emph{NN}} switch

@geindex gnat1

@code{gcc} is actually a driver program that looks at the extensions of
the file arguments and loads the appropriate compiler. For example, the
GNU C compiler is @code{cc1}, and the Ada compiler is @code{gnat1}.
These programs are in directories known to the driver program (in some
configurations via environment variables you set), but need not be in
your path. The @code{gcc} driver also calls the assembler and any other
utilities needed to complete the generation of the required object
files.

It is possible to supply several file names on the same @code{gcc}
command. This causes @code{gcc} to call the appropriate compiler for
each file. For example, the following command lists two separate
files to be compiled:

@example
$ gcc -c x.adb y.adb
@end example

calls @code{gnat1} (the Ada compiler) twice to compile @code{x.adb} and
@code{y.adb}.
The compiler generates two object files @code{x.o} and @code{y.o}
and the two ALI files @code{x.ali} and @code{y.ali}.

Any switches apply to all the files listed, see @ref{ea,,Compiler Switches} for a
list of available @code{gcc} switches.

@node Search Paths and the Run-Time Library RTL,Order of Compilation Issues,Compiling Programs,Compiling with gcc
@anchor{gnat_ugn/building_executable_programs_with_gnat id10}@anchor{eb}@anchor{gnat_ugn/building_executable_programs_with_gnat search-paths-and-the-run-time-library-rtl}@anchor{89}
@subsection Search Paths and the Run-Time Library (RTL)


With the GNAT source-based library system, the compiler must be able to
find source files for units that are needed by the unit being compiled.
Search paths are used to guide this process.

The compiler compiles one source file whose name must be given
explicitly on the command line. In other words, no searching is done
for this file. To find all other source files that are needed (the most
common being the specs of units), the compiler examines the following
directories, in the following order:


@itemize *

@item 
The directory containing the source file of the main unit being compiled
(the file name on the command line).

@item 
Each directory named by an @code{-I} switch given on the @code{gcc}
command line, in the order given.

@geindex ADA_PRJ_INCLUDE_FILE

@item 
Each of the directories listed in the text file whose name is given
by the 
@geindex ADA_PRJ_INCLUDE_FILE
@geindex environment variable; ADA_PRJ_INCLUDE_FILE
@code{ADA_PRJ_INCLUDE_FILE} environment variable.
@geindex ADA_PRJ_INCLUDE_FILE
@geindex environment variable; ADA_PRJ_INCLUDE_FILE
@code{ADA_PRJ_INCLUDE_FILE} is normally set by gnatmake or by the gnat
driver when project files are used. It should not normally be set
by other means.

@geindex ADA_INCLUDE_PATH

@item 
Each of the directories listed in the value of the
@geindex ADA_INCLUDE_PATH
@geindex environment variable; ADA_INCLUDE_PATH
@code{ADA_INCLUDE_PATH} environment variable.
Construct this value
exactly as the 
@geindex PATH
@geindex environment variable; PATH
@code{PATH} environment variable: a list of directory
names separated by colons (semicolons when working with the NT version).

@item 
The content of the @code{ada_source_path} file which is part of the GNAT
installation tree and is used to store standard libraries such as the
GNAT Run Time Library (RTL) source files.
@ref{87,,Installing a library}
@end itemize

Specifying the switch @code{-I-}
inhibits the use of the directory
containing the source file named in the command line. You can still
have this directory on your search path, but in this case it must be
explicitly requested with a @code{-I} switch.

Specifying the switch @code{-nostdinc}
inhibits the search of the default location for the GNAT Run Time
Library (RTL) source files.

The compiler outputs its object files and ALI files in the current
working directory.
Caution: The object file can be redirected with the @code{-o} switch;
however, @code{gcc} and @code{gnat1} have not been coordinated on this
so the @code{ALI} file will not go to the right place. Therefore, you should
avoid using the @code{-o} switch.

@geindex System.IO

The packages @code{Ada}, @code{System}, and @code{Interfaces} and their
children make up the GNAT RTL, together with the simple @code{System.IO}
package used in the @code{"Hello World"} example. The sources for these units
are needed by the compiler and are kept together in one directory. Not
all of the bodies are needed, but all of the sources are kept together
anyway. In a normal installation, you need not specify these directory
names when compiling or binding. Either the environment variables or
the built-in defaults cause these files to be found.

In addition to the language-defined hierarchies (@code{System}, @code{Ada} and
@code{Interfaces}), the GNAT distribution provides a fourth hierarchy,
consisting of child units of @code{GNAT}. This is a collection of generally
useful types, subprograms, etc. See the @cite{GNAT_Reference_Manual}
for further details.

Besides simplifying access to the RTL, a major use of search paths is
in compiling sources from multiple directories. This can make
development environments much more flexible.

@node Order of Compilation Issues,Examples,Search Paths and the Run-Time Library RTL,Compiling with gcc
@anchor{gnat_ugn/building_executable_programs_with_gnat id11}@anchor{ec}@anchor{gnat_ugn/building_executable_programs_with_gnat order-of-compilation-issues}@anchor{ed}
@subsection Order of Compilation Issues


If, in our earlier example, there was a spec for the @code{hello}
procedure, it would be contained in the file @code{hello.ads}; yet this
file would not have to be explicitly compiled. This is the result of the
model we chose to implement library management. Some of the consequences
of this model are as follows:


@itemize *

@item 
There is no point in compiling specs (except for package
specs with no bodies) because these are compiled as needed by clients. If
you attempt a useless compilation, you will receive an error message.
It is also useless to compile subunits because they are compiled as needed
by the parent.

@item 
There are no order of compilation requirements: performing a
compilation never obsoletes anything. The only way you can obsolete
something and require recompilations is to modify one of the
source files on which it depends.

@item 
There is no library as such, apart from the ALI files
(@ref{42,,The Ada Library Information Files}, for information on the format
of these files). For now we find it convenient to create separate ALI files,
but eventually the information therein may be incorporated into the object
file directly.

@item 
When you compile a unit, the source files for the specs of all units
that it @emph{with}s, all its subunits, and the bodies of any generics it
instantiates must be available (reachable by the search-paths mechanism
described above), or you will receive a fatal error message.
@end itemize

@node Examples,,Order of Compilation Issues,Compiling with gcc
@anchor{gnat_ugn/building_executable_programs_with_gnat id12}@anchor{ee}@anchor{gnat_ugn/building_executable_programs_with_gnat examples}@anchor{ef}
@subsection Examples


The following are some typical Ada compilation command line examples:

@example
$ gcc -c xyz.adb
@end example

Compile body in file @code{xyz.adb} with all default options.

@example
$ gcc -c -O2 -gnata xyz-def.adb
@end example

Compile the child unit package in file @code{xyz-def.adb} with extensive
optimizations, and pragma @code{Assert}/@cite{Debug} statements
enabled.

@example
$ gcc -c -gnatc abc-def.adb
@end example

Compile the subunit in file @code{abc-def.adb} in semantic-checking-only
mode.

@node Compiler Switches,Linker Switches,Compiling with gcc,Building Executable Programs with GNAT
@anchor{gnat_ugn/building_executable_programs_with_gnat compiler-switches}@anchor{f0}@anchor{gnat_ugn/building_executable_programs_with_gnat switches-for-gcc}@anchor{ea}
@section Compiler Switches


The @code{gcc} command accepts switches that control the
compilation process. These switches are fully described in this section:
first an alphabetical listing of all switches with a brief description,
and then functionally grouped sets of switches with more detailed
information.

More switches exist for GCC than those documented here, especially
for specific targets. However, their use is not recommended as
they may change code generation in ways that are incompatible with
the Ada run-time library, or can cause inconsistencies between
compilation units.

@menu
* Alphabetical List of All Switches:: 
* Output and Error Message Control:: 
* Warning Message Control:: 
* Debugging and Assertion Control:: 
* Validity Checking:: 
* Style Checking:: 
* Run-Time Checks:: 
* Using gcc for Syntax Checking:: 
* Using gcc for Semantic Checking:: 
* Compiling Different Versions of Ada:: 
* Character Set Control:: 
* File Naming Control:: 
* Subprogram Inlining Control:: 
* Auxiliary Output Control:: 
* Debugging Control:: 
* Exception Handling Control:: 
* Units to Sources Mapping Files:: 
* Code Generation Control:: 

@end menu

@node Alphabetical List of All Switches,Output and Error Message Control,,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat id13}@anchor{f1}@anchor{gnat_ugn/building_executable_programs_with_gnat alphabetical-list-of-all-switches}@anchor{f2}
@subsection Alphabetical List of All Switches


@geindex -b (gcc)


@table @asis

@item @code{-b @emph{target}}

Compile your program to run on @code{target}, which is the name of a
system configuration. You must have a GNAT cross-compiler built if
@code{target} is not the same as your host system.
@end table

@geindex -B (gcc)


@table @asis

@item @code{-B@emph{dir}}

Load compiler executables (for example, @code{gnat1}, the Ada compiler)
from @code{dir} instead of the default location. Only use this switch
when multiple versions of the GNAT compiler are available.
See the "Options for Directory Search" section in the
@cite{Using the GNU Compiler Collection (GCC)} manual for further details.
You would normally use the @code{-b} or @code{-V} switch instead.
@end table

@geindex -c (gcc)


@table @asis

@item @code{-c}

Compile. Always use this switch when compiling Ada programs.

Note: for some other languages when using @code{gcc}, notably in
the case of C and C++, it is possible to use
use @code{gcc} without a @code{-c} switch to
compile and link in one step. In the case of GNAT, you
cannot use this approach, because the binder must be run
and @code{gcc} cannot be used to run the GNAT binder.
@end table

@geindex -fcallgraph-info (gcc)


@table @asis

@item @code{-fcallgraph-info[=su,da]}

Makes the compiler output callgraph information for the program, on a
per-file basis. The information is generated in the VCG format.  It can
be decorated with additional, per-node and/or per-edge information, if a
list of comma-separated markers is additionally specified. When the
@code{su} marker is specified, the callgraph is decorated with stack usage
information; it is equivalent to @code{-fstack-usage}. When the @code{da}
marker is specified, the callgraph is decorated with information about
dynamically allocated objects.
@end table

@geindex -fdump-scos (gcc)


@table @asis

@item @code{-fdump-scos}

Generates SCO (Source Coverage Obligation) information in the ALI file.
This information is used by advanced coverage tools. See unit @code{SCOs}
in the compiler sources for details in files @code{scos.ads} and
@code{scos.adb}.
@end table

@geindex -flto (gcc)


@table @asis

@item @code{-flto[=@emph{n}]}

Enables Link Time Optimization. This switch must be used in conjunction
with the @code{-Ox} switches (but not with the @code{-gnatn} switch
since it is a full replacement for the latter) and instructs the compiler
to defer most optimizations until the link stage. The advantage of this
approach is that the compiler can do a whole-program analysis and choose
the best interprocedural optimization strategy based on a complete view
of the program, instead of a fragmentary view with the usual approach.
This can also speed up the compilation of big programs and reduce the
size of the executable, compared with a traditional per-unit compilation
with inlining across units enabled by the @code{-gnatn} switch.
The drawback of this approach is that it may require more memory and that
the debugging information generated by -g with it might be hardly usable.
The switch, as well as the accompanying @code{-Ox} switches, must be
specified both for the compilation and the link phases.
If the @code{n} parameter is specified, the optimization and final code
generation at link time are executed using @code{n} parallel jobs by
means of an installed @code{make} program.
@end table

@geindex -fno-inline (gcc)


@table @asis

@item @code{-fno-inline}

Suppresses all inlining, unless requested with pragma @code{Inline_Always}. The
effect is enforced regardless of other optimization or inlining switches.
Note that inlining can also be suppressed on a finer-grained basis with
pragma @code{No_Inline}.
@end table

@geindex -fno-inline-functions (gcc)


@table @asis

@item @code{-fno-inline-functions}

Suppresses automatic inlining of subprograms, which is enabled
if @code{-O3} is used.
@end table

@geindex -fno-inline-small-functions (gcc)


@table @asis

@item @code{-fno-inline-small-functions}

Suppresses automatic inlining of small subprograms, which is enabled
if @code{-O2} is used.
@end table

@geindex -fno-inline-functions-called-once (gcc)


@table @asis

@item @code{-fno-inline-functions-called-once}

Suppresses inlining of subprograms local to the unit and called once
from within it, which is enabled if @code{-O1} is used.
@end table

@geindex -fno-ivopts (gcc)


@table @asis

@item @code{-fno-ivopts}

Suppresses high-level loop induction variable optimizations, which are
enabled if @code{-O1} is used. These optimizations are generally
profitable but, for some specific cases of loops with numerous uses
of the iteration variable that follow a common pattern, they may end
up destroying the regularity that could be exploited at a lower level
and thus producing inferior code.
@end table

@geindex -fno-strict-aliasing (gcc)


@table @asis

@item @code{-fno-strict-aliasing}

Causes the compiler to avoid assumptions regarding non-aliasing
of objects of different types. See
@ref{f3,,Optimization and Strict Aliasing} for details.
@end table

@geindex -fno-strict-overflow (gcc)


@table @asis

@item @code{-fno-strict-overflow}

Causes the compiler to avoid assumptions regarding the rules of signed
integer overflow. These rules specify that signed integer overflow will
result in a Constraint_Error exception at run time and are enforced in
default mode by the compiler, so this switch should not be necessary in
normal operating mode. It might be useful in conjunction with @code{-gnato0}
for very peculiar cases of low-level programming.
@end table

@geindex -fstack-check (gcc)


@table @asis

@item @code{-fstack-check}

Activates stack checking.
See @ref{f4,,Stack Overflow Checking} for details.
@end table

@geindex -fstack-usage (gcc)


@table @asis

@item @code{-fstack-usage}

Makes the compiler output stack usage information for the program, on a
per-subprogram basis. See @ref{f5,,Static Stack Usage Analysis} for details.
@end table

@geindex -g (gcc)


@table @asis

@item @code{-g}

Generate debugging information. This information is stored in the object
file and copied from there to the final executable file by the linker,
where it can be read by the debugger. You must use the
@code{-g} switch if you plan on using the debugger.
@end table

@geindex -gnat05 (gcc)


@table @asis

@item @code{-gnat05}

Allow full Ada 2005 features.
@end table

@geindex -gnat12 (gcc)


@table @asis

@item @code{-gnat12}

Allow full Ada 2012 features.
@end table

@geindex -gnat83 (gcc)

@geindex -gnat2005 (gcc)


@table @asis

@item @code{-gnat2005}

Allow full Ada 2005 features (same as @code{-gnat05})
@end table

@geindex -gnat2012 (gcc)


@table @asis

@item @code{-gnat2012}

Allow full Ada 2012 features (same as @code{-gnat12})

@item @code{-gnat83}

Enforce Ada 83 restrictions.
@end table

@geindex -gnat95 (gcc)


@table @asis

@item @code{-gnat95}

Enforce Ada 95 restrictions.

Note: for compatibility with some Ada 95 compilers which support only
the @code{overriding} keyword of Ada 2005, the @code{-gnatd.D} switch can
be used along with @code{-gnat95} to achieve a similar effect with GNAT.

@code{-gnatd.D} instructs GNAT to consider @code{overriding} as a keyword
and handle its associated semantic checks, even in Ada 95 mode.
@end table

@geindex -gnata (gcc)


@table @asis

@item @code{-gnata}

Assertions enabled. @code{Pragma Assert} and @code{pragma Debug} to be
activated. Note that these pragmas can also be controlled using the
configuration pragmas @code{Assertion_Policy} and @code{Debug_Policy}.
It also activates pragmas @code{Check}, @code{Precondition}, and
@code{Postcondition}. Note that these pragmas can also be controlled
using the configuration pragma @code{Check_Policy}. In Ada 2012, it
also activates all assertions defined in the RM as aspects: preconditions,
postconditions, type invariants and (sub)type predicates. In all Ada modes,
corresponding pragmas for type invariants and (sub)type predicates are
also activated. The default is that all these assertions are disabled,
and have no effect, other than being checked for syntactic validity, and
in the case of subtype predicates, constructions such as membership tests
still test predicates even if assertions are turned off.
@end table

@geindex -gnatA (gcc)


@table @asis

@item @code{-gnatA}

Avoid processing @code{gnat.adc}. If a @code{gnat.adc} file is present,
it will be ignored.
@end table

@geindex -gnatb (gcc)


@table @asis

@item @code{-gnatb}

Generate brief messages to @code{stderr} even if verbose mode set.
@end table

@geindex -gnatB (gcc)


@table @asis

@item @code{-gnatB}

Assume no invalid (bad) values except for 'Valid attribute use
(@ref{f6,,Validity Checking}).
@end table

@geindex -gnatc (gcc)


@table @asis

@item @code{-gnatc}

Check syntax and semantics only (no code generation attempted). When the
compiler is invoked by @code{gnatmake}, if the switch @code{-gnatc} is
only given to the compiler (after @code{-cargs} or in package Compiler of
the project file, @code{gnatmake} will fail because it will not find the
object file after compilation. If @code{gnatmake} is called with
@code{-gnatc} as a builder switch (before @code{-cargs} or in package
Builder of the project file) then @code{gnatmake} will not fail because
it will not look for the object files after compilation, and it will not try
to build and link.
@end table

@geindex -gnatC (gcc)


@table @asis

@item @code{-gnatC}

Generate CodePeer intermediate format (no code generation attempted).
This switch will generate an intermediate representation suitable for
use by CodePeer (@code{.scil} files). This switch is not compatible with
code generation (it will, among other things, disable some switches such
as -gnatn, and enable others such as -gnata).
@end table

@geindex -gnatd (gcc)


@table @asis

@item @code{-gnatd}

Specify debug options for the compiler. The string of characters after
the @code{-gnatd} specify the specific debug options. The possible
characters are 0-9, a-z, A-Z, optionally preceded by a dot. See
compiler source file @code{debug.adb} for details of the implemented
debug options. Certain debug options are relevant to applications
programmers, and these are documented at appropriate points in this
users guide.
@end table

@geindex -gnatD[nn] (gcc)


@table @asis

@item @code{-gnatD}

Create expanded source files for source level debugging. This switch
also suppresses generation of cross-reference information
(see @code{-gnatx}). Note that this switch is not allowed if a previous
-gnatR switch has been given, since these two switches are not compatible.
@end table

@geindex -gnateA (gcc)


@table @asis

@item @code{-gnateA}

Check that the actual parameters of a subprogram call are not aliases of one
another. To qualify as aliasing, the actuals must denote objects of a composite
type, their memory locations must be identical or overlapping, and at least one
of the corresponding formal parameters must be of mode OUT or IN OUT.

@example
type Rec_Typ is record
   Data : Integer := 0;
end record;

function Self (Val : Rec_Typ) return Rec_Typ is
begin
   return Val;
end Self;

procedure Detect_Aliasing (Val_1 : in out Rec_Typ; Val_2 : Rec_Typ) is
begin
   null;
end Detect_Aliasing;

Obj : Rec_Typ;

Detect_Aliasing (Obj, Obj);
Detect_Aliasing (Obj, Self (Obj));
@end example

In the example above, the first call to @code{Detect_Aliasing} fails with a
@code{Program_Error} at run time because the actuals for @code{Val_1} and
@code{Val_2} denote the same object. The second call executes without raising
an exception because @code{Self(Obj)} produces an anonymous object which does
not share the memory location of @code{Obj}.
@end table

@geindex -gnatec (gcc)


@table @asis

@item @code{-gnatec=@emph{path}}

Specify a configuration pragma file
(the equal sign is optional)
(@ref{79,,The Configuration Pragmas Files}).
@end table

@geindex -gnateC (gcc)


@table @asis

@item @code{-gnateC}

Generate CodePeer messages in a compiler-like format. This switch is only
effective if @code{-gnatcC} is also specified and requires an installation
of CodePeer.
@end table

@geindex -gnated (gcc)


@table @asis

@item @code{-gnated}

Disable atomic synchronization
@end table

@geindex -gnateD (gcc)


@table @asis

@item @code{-gnateDsymbol[=@emph{value}]}

Defines a symbol, associated with @code{value}, for preprocessing.
(@ref{18,,Integrated Preprocessing}).
@end table

@geindex -gnateE (gcc)


@table @asis

@item @code{-gnateE}

Generate extra information in exception messages. In particular, display
extra column information and the value and range associated with index and
range check failures, and extra column information for access checks.
In cases where the compiler is able to determine at compile time that
a check will fail, it gives a warning, and the extra information is not
produced at run time.
@end table

@geindex -gnatef (gcc)


@table @asis

@item @code{-gnatef}

Display full source path name in brief error messages.
@end table

@geindex -gnateF (gcc)


@table @asis

@item @code{-gnateF}

Check for overflow on all floating-point operations, including those
for unconstrained predefined types. See description of pragma
@code{Check_Float_Overflow} in GNAT RM.
@end table

@geindex -gnateg (gcc)

@code{-gnateg}
@code{-gnatceg}

@quotation

The @code{-gnatc} switch must always be specified before this switch, e.g.
@code{-gnatceg}. Generate a C header from the Ada input file. See
@ref{ca,,Generating C Headers for Ada Specifications} for more
information.
@end quotation

@geindex -gnateG (gcc)


@table @asis

@item @code{-gnateG}

Save result of preprocessing in a text file.
@end table

@geindex -gnatei (gcc)


@table @asis

@item @code{-gnatei@emph{nnn}}

Set maximum number of instantiations during compilation of a single unit to
@code{nnn}. This may be useful in increasing the default maximum of 8000 for
the rare case when a single unit legitimately exceeds this limit.
@end table

@geindex -gnateI (gcc)


@table @asis

@item @code{-gnateI@emph{nnn}}

Indicates that the source is a multi-unit source and that the index of the
unit to compile is @code{nnn}. @code{nnn} needs to be a positive number and need
to be a valid index in the multi-unit source.
@end table

@geindex -gnatel (gcc)


@table @asis

@item @code{-gnatel}

This switch can be used with the static elaboration model to issue info
messages showing
where implicit @code{pragma Elaborate} and @code{pragma Elaborate_All}
are generated. This is useful in diagnosing elaboration circularities
caused by these implicit pragmas when using the static elaboration
model. See See the section in this guide on elaboration checking for
further details. These messages are not generated by default, and are
intended only for temporary use when debugging circularity problems.
@end table

@geindex -gnatel (gcc)


@table @asis

@item @code{-gnateL}

This switch turns off the info messages about implicit elaboration pragmas.
@end table

@geindex -gnatem (gcc)


@table @asis

@item @code{-gnatem=@emph{path}}

Specify a mapping file
(the equal sign is optional)
(@ref{f7,,Units to Sources Mapping Files}).
@end table

@geindex -gnatep (gcc)


@table @asis

@item @code{-gnatep=@emph{file}}

Specify a preprocessing data file
(the equal sign is optional)
(@ref{18,,Integrated Preprocessing}).
@end table

@geindex -gnateP (gcc)


@table @asis

@item @code{-gnateP}

Turn categorization dependency errors into warnings.
Ada requires that units that WITH one another have compatible categories, for
example a Pure unit cannot WITH a Preelaborate unit. If this switch is used,
these errors become warnings (which can be ignored, or suppressed in the usual
manner). This can be useful in some specialized circumstances such as the
temporary use of special test software.
@end table

@geindex -gnateS (gcc)


@table @asis

@item @code{-gnateS}

Synonym of @code{-fdump-scos}, kept for backwards compatibility.
@end table

@geindex -gnatet=file (gcc)


@table @asis

@item @code{-gnatet=@emph{path}}

Generate target dependent information. The format of the output file is
described in the section about switch @code{-gnateT}.
@end table

@geindex -gnateT (gcc)


@table @asis

@item @code{-gnateT=@emph{path}}

Read target dependent information, such as endianness or sizes and alignments
of base type. If this switch is passed, the default target dependent
information of the compiler is replaced by the one read from the input file.
This is used by tools other than the compiler, e.g. to do
semantic analysis of programs that will run on some other target than
the machine on which the tool is run.

The following target dependent values should be defined,
where @code{Nat} denotes a natural integer value, @code{Pos} denotes a
positive integer value, and fields marked with a question mark are
boolean fields, where a value of 0 is False, and a value of 1 is True:

@example
Bits_BE                    : Nat; -- Bits stored big-endian?
Bits_Per_Unit              : Pos; -- Bits in a storage unit
Bits_Per_Word              : Pos; -- Bits in a word
Bytes_BE                   : Nat; -- Bytes stored big-endian?
Char_Size                  : Pos; -- Standard.Character'Size
Double_Float_Alignment     : Nat; -- Alignment of double float
Double_Scalar_Alignment    : Nat; -- Alignment of double length scalar
Double_Size                : Pos; -- Standard.Long_Float'Size
Float_Size                 : Pos; -- Standard.Float'Size
Float_Words_BE             : Nat; -- Float words stored big-endian?
Int_Size                   : Pos; -- Standard.Integer'Size
Long_Double_Size           : Pos; -- Standard.Long_Long_Float'Size
Long_Long_Size             : Pos; -- Standard.Long_Long_Integer'Size
Long_Size                  : Pos; -- Standard.Long_Integer'Size
Maximum_Alignment          : Pos; -- Maximum permitted alignment
Max_Unaligned_Field        : Pos; -- Maximum size for unaligned bit field
Pointer_Size               : Pos; -- System.Address'Size
Short_Enums                : Nat; -- Foreign enums use short size?
Short_Size                 : Pos; -- Standard.Short_Integer'Size
Strict_Alignment           : Nat; -- Strict alignment?
System_Allocator_Alignment : Nat; -- Alignment for malloc calls
Wchar_T_Size               : Pos; -- Interfaces.C.wchar_t'Size
Words_BE                   : Nat; -- Words stored big-endian?
@end example

@code{Bits_Per_Unit} is the number of bits in a storage unit, the equivalent of
GCC macro @code{BITS_PER_UNIT} documented as follows: @cite{Define this macro to be the number of bits in an addressable storage unit (byte); normally 8.}

@code{Bits_Per_Word} is the number of bits in a machine word, the equivalent of
GCC macro @code{BITS_PER_WORD} documented as follows: @cite{Number of bits in a word; normally 32.}

@code{Double_Scalar_Alignment} is the alignment for a scalar whose size is two
machine words. It should be the same as the alignment for C @code{long_long} on
most targets.

@code{Maximum_Alignment} is the maximum alignment that the compiler might choose
by default for a type or object, which is also the maximum alignment that can
be specified in GNAT. It is computed for GCC backends as @code{BIGGEST_ALIGNMENT
/ BITS_PER_UNIT} where GCC macro @code{BIGGEST_ALIGNMENT} is documented as
follows: @cite{Biggest alignment that any data type can require on this machine@comma{} in bits.}

@code{Max_Unaligned_Field} is the maximum size for unaligned bit field, which is
64 for the majority of GCC targets (but can be different on some targets like
AAMP).

@code{Strict_Alignment} is the equivalent of GCC macro @code{STRICT_ALIGNMENT}
documented as follows: @cite{Define this macro to be the value 1 if instructions will fail to work if given data not on the nominal alignment. If instructions will merely go slower in that case@comma{} define this macro as 0.}

@code{System_Allocator_Alignment} is the guaranteed alignment of data returned
by calls to @code{malloc}.

The format of the input file is as follows. First come the values of
the variables defined above, with one line per value:

@example
name  value
@end example

where @code{name} is the name of the parameter, spelled out in full,
and cased as in the above list, and @code{value} is an unsigned decimal
integer. Two or more blanks separates the name from the value.

All the variables must be present, in alphabetical order (i.e. the
same order as the list above).

Then there is a blank line to separate the two parts of the file. Then
come the lines showing the floating-point types to be registered, with
one line per registered mode:

@example
name  digs float_rep size alignment
@end example

where @code{name} is the string name of the type (which can have
single spaces embedded in the name (e.g. long double), @code{digs} is
the number of digits for the floating-point type, @code{float_rep} is
the float representation (I/V/A for IEEE-754-Binary, Vax_Native,
AAMP), @code{size} is the size in bits, @code{alignment} is the
alignment in bits. The name is followed by at least two blanks, fields
are separated by at least one blank, and a LF character immediately
follows the alignment field.

Here is an example of a target parameterization file:

@example
Bits_BE                       0
Bits_Per_Unit                 8
Bits_Per_Word                64
Bytes_BE                      0
Char_Size                     8
Double_Float_Alignment        0
Double_Scalar_Alignment       0
Double_Size                  64
Float_Size                   32
Float_Words_BE                0
Int_Size                     64
Long_Double_Size            128
Long_Long_Size               64
Long_Size                    64
Maximum_Alignment            16
Max_Unaligned_Field          64
Pointer_Size                 64
Short_Size                   16
Strict_Alignment              0
System_Allocator_Alignment   16
Wchar_T_Size                 32
Words_BE                      0

float         15  I  64  64
double        15  I  64  64
long double   18  I  80 128
TF            33  I 128 128
@end example
@end table

@geindex -gnateu (gcc)


@table @asis

@item @code{-gnateu}

Ignore unrecognized validity, warning, and style switches that
appear after this switch is given. This may be useful when
compiling sources developed on a later version of the compiler
with an earlier version. Of course the earlier version must
support this switch.
@end table

@geindex -gnateV (gcc)


@table @asis

@item @code{-gnateV}

Check that all actual parameters of a subprogram call are valid according to
the rules of validity checking (@ref{f6,,Validity Checking}).
@end table

@geindex -gnateY (gcc)


@table @asis

@item @code{-gnateY}

Ignore all STYLE_CHECKS pragmas. Full legality checks
are still carried out, but the pragmas have no effect
on what style checks are active. This allows all style
checking options to be controlled from the command line.
@end table

@geindex -gnatE (gcc)


@table @asis

@item @code{-gnatE}

Full dynamic elaboration checks.
@end table

@geindex -gnatf (gcc)


@table @asis

@item @code{-gnatf}

Full errors. Multiple errors per line, all undefined references, do not
attempt to suppress cascaded errors.
@end table

@geindex -gnatF (gcc)


@table @asis

@item @code{-gnatF}

Externals names are folded to all uppercase.
@end table

@geindex -gnatg (gcc)


@table @asis

@item @code{-gnatg}

Internal GNAT implementation mode. This should not be used for applications
programs, it is intended only for use by the compiler and its run-time
library. For documentation, see the GNAT sources. Note that @code{-gnatg}
implies @code{-gnatw.ge} and @code{-gnatyg} so that all standard
warnings and all standard style options are turned on. All warnings and style
messages are treated as errors.
@end table

@geindex -gnatG[nn] (gcc)


@table @asis

@item @code{-gnatG=nn}

List generated expanded code in source form.
@end table

@geindex -gnath (gcc)


@table @asis

@item @code{-gnath}

Output usage information. The output is written to @code{stdout}.
@end table

@geindex -gnatH (gcc)


@table @asis

@item @code{-gnatH}

Legacy elaboration-checking mode enabled. When this switch is in effect, the
pre-18.x access-before-elaboration model becomes the de facto model.
@end table

@geindex -gnati (gcc)


@table @asis

@item @code{-gnati@emph{c}}

Identifier character set (@code{c} = 1/2/3/4/8/9/p/f/n/w).
For details of the possible selections for @code{c},
see @ref{48,,Character Set Control}.
@end table

@geindex -gnatI (gcc)


@table @asis

@item @code{-gnatI}

Ignore representation clauses. When this switch is used,
representation clauses are treated as comments. This is useful
when initially porting code where you want to ignore rep clause
problems, and also for compiling foreign code (particularly
for use with ASIS). The representation clauses that are ignored
are: enumeration_representation_clause, record_representation_clause,
and attribute_definition_clause for the following attributes:
Address, Alignment, Bit_Order, Component_Size, Machine_Radix,
Object_Size, Scalar_Storage_Order, Size, Small, Stream_Size,
and Value_Size. Pragma Default_Scalar_Storage_Order is also ignored.
Note that this option should be used only for compiling -- the
code is likely to malfunction at run time.

Note that when @code{-gnatct} is used to generate trees for input
into ASIS tools, these representation clauses are removed
from the tree and ignored. This means that the tool will not see them.
@end table

@geindex -gnatjnn (gcc)


@table @asis

@item @code{-gnatj@emph{nn}}

Reformat error messages to fit on @code{nn} character lines
@end table

@geindex -gnatJ (gcc)


@table @asis

@item @code{-gnatJ}

Permissive elaboration-checking mode enabled. When this switch is in effect,
the post-18.x access-before-elaboration model ignores potential issues with:


@itemize -

@item 
Accept statements

@item 
Activations of tasks defined in instances

@item 
Assertion pragmas

@item 
Calls from within an instance to its enclosing context

@item 
Calls through generic formal parameters

@item 
Calls to subprograms defined in instances

@item 
Entry calls

@item 
Indirect calls using 'Access

@item 
Requeue statements

@item 
Select statements

@item 
Synchronous task suspension
@end itemize

and does not emit compile-time diagnostics or run-time checks.
@end table

@geindex -gnatk (gcc)


@table @asis

@item @code{-gnatk=@emph{n}}

Limit file names to @code{n} (1-999) characters (@code{k} = krunch).
@end table

@geindex -gnatl (gcc)


@table @asis

@item @code{-gnatl}

Output full source listing with embedded error messages.
@end table

@geindex -gnatL (gcc)


@table @asis

@item @code{-gnatL}

Used in conjunction with -gnatG or -gnatD to intersperse original
source lines (as comment lines with line numbers) in the expanded
source output.
@end table

@geindex -gnatm (gcc)


@table @asis

@item @code{-gnatm=@emph{n}}

Limit number of detected error or warning messages to @code{n}
where @code{n} is in the range 1..999999. The default setting if
no switch is given is 9999. If the number of warnings reaches this
limit, then a message is output and further warnings are suppressed,
but the compilation is continued. If the number of error messages
reaches this limit, then a message is output and the compilation
is abandoned. The equal sign here is optional. A value of zero
means that no limit applies.
@end table

@geindex -gnatn (gcc)


@table @asis

@item @code{-gnatn[12]}

Activate inlining across units for subprograms for which pragma @code{Inline}
is specified. This inlining is performed by the GCC back-end. An optional
digit sets the inlining level: 1 for moderate inlining across units
or 2 for full inlining across units. If no inlining level is specified,
the compiler will pick it based on the optimization level.
@end table

@geindex -gnatN (gcc)


@table @asis

@item @code{-gnatN}

Activate front end inlining for subprograms for which
pragma @code{Inline} is specified. This inlining is performed
by the front end and will be visible in the
@code{-gnatG} output.

When using a gcc-based back end (in practice this means using any version
of GNAT other than the JGNAT, .NET or GNAAMP versions), then the use of
@code{-gnatN} is deprecated, and the use of @code{-gnatn} is preferred.
Historically front end inlining was more extensive than the gcc back end
inlining, but that is no longer the case.
@end table

@geindex -gnato0 (gcc)


@table @asis

@item @code{-gnato0}

Suppresses overflow checking. This causes the behavior of the compiler to
match the default for older versions where overflow checking was suppressed
by default. This is equivalent to having
@code{pragma Suppress (Overflow_Check)} in a configuration pragma file.
@end table

@geindex -gnato?? (gcc)


@table @asis

@item @code{-gnato??}

Set default mode for handling generation of code to avoid intermediate
arithmetic overflow. Here @code{??} is two digits, a
single digit, or nothing. Each digit is one of the digits @code{1}
through @code{3}:


@multitable {xxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} 
@item

Digit

@tab

Interpretation

@item

@emph{1}

@tab

All intermediate overflows checked against base type (@code{STRICT})

@item

@emph{2}

@tab

Minimize intermediate overflows (@code{MINIMIZED})

@item

@emph{3}

@tab

Eliminate intermediate overflows (@code{ELIMINATED})

@end multitable


If only one digit appears, then it applies to all
cases; if two digits are given, then the first applies outside
assertions, pre/postconditions, and type invariants, and the second
applies within assertions, pre/postconditions, and type invariants.

If no digits follow the @code{-gnato}, then it is equivalent to
@code{-gnato11},
causing all intermediate overflows to be handled in strict
mode.

This switch also causes arithmetic overflow checking to be performed
(as though @code{pragma Unsuppress (Overflow_Check)} had been specified).

The default if no option @code{-gnato} is given is that overflow handling
is in @code{STRICT} mode (computations done using the base type), and that
overflow checking is enabled.

Note that division by zero is a separate check that is not
controlled by this switch (divide-by-zero checking is on by default).

See also @ref{f8,,Specifying the Desired Mode}.
@end table

@geindex -gnatp (gcc)


@table @asis

@item @code{-gnatp}

Suppress all checks. See @ref{f9,,Run-Time Checks} for details. This switch
has no effect if cancelled by a subsequent @code{-gnat-p} switch.
@end table

@geindex -gnat-p (gcc)


@table @asis

@item @code{-gnat-p}

Cancel effect of previous @code{-gnatp} switch.
@end table

@geindex -gnatP (gcc)


@table @asis

@item @code{-gnatP}

Enable polling. This is required on some systems (notably Windows NT) to
obtain asynchronous abort and asynchronous transfer of control capability.
See @code{Pragma_Polling} in the @cite{GNAT_Reference_Manual} for full
details.
@end table

@geindex -gnatq (gcc)


@table @asis

@item @code{-gnatq}

Don't quit. Try semantics, even if parse errors.
@end table

@geindex -gnatQ (gcc)


@table @asis

@item @code{-gnatQ}

Don't quit. Generate @code{ALI} and tree files even if illegalities.
Note that code generation is still suppressed in the presence of any
errors, so even with @code{-gnatQ} no object file is generated.
@end table

@geindex -gnatr (gcc)


@table @asis

@item @code{-gnatr}

Treat pragma Restrictions as Restriction_Warnings.
@end table

@geindex -gnatR (gcc)


@table @asis

@item @code{-gnatR[0|1|2|3][e][j][m][s]}

Output representation information for declared types, objects and
subprograms. Note that this switch is not allowed if a previous
@code{-gnatD} switch has been given, since these two switches
are not compatible.
@end table

@geindex -gnats (gcc)


@table @asis

@item @code{-gnats}

Syntax check only.
@end table

@geindex -gnatS (gcc)


@table @asis

@item @code{-gnatS}

Print package Standard.
@end table

@geindex -gnatt (gcc)


@table @asis

@item @code{-gnatt}

Generate tree output file.
@end table

@geindex -gnatT (gcc)


@table @asis

@item @code{-gnatT@emph{nnn}}

All compiler tables start at @code{nnn} times usual starting size.
@end table

@geindex -gnatu (gcc)


@table @asis

@item @code{-gnatu}

List units for this compilation.
@end table

@geindex -gnatU (gcc)


@table @asis

@item @code{-gnatU}

Tag all error messages with the unique string 'error:'
@end table

@geindex -gnatv (gcc)


@table @asis

@item @code{-gnatv}

Verbose mode. Full error output with source lines to @code{stdout}.
@end table

@geindex -gnatV (gcc)


@table @asis

@item @code{-gnatV}

Control level of validity checking (@ref{f6,,Validity Checking}).
@end table

@geindex -gnatw (gcc)


@table @asis

@item @code{-gnatw@emph{xxx}}

Warning mode where
@code{xxx} is a string of option letters that denotes
the exact warnings that
are enabled or disabled (@ref{fa,,Warning Message Control}).
@end table

@geindex -gnatW (gcc)


@table @asis

@item @code{-gnatW@emph{e}}

Wide character encoding method
(@code{e}=n/h/u/s/e/8).
@end table

@geindex -gnatx (gcc)


@table @asis

@item @code{-gnatx}

Suppress generation of cross-reference information.
@end table

@geindex -gnatX (gcc)


@table @asis

@item @code{-gnatX}

Enable GNAT implementation extensions and latest Ada version.
@end table

@geindex -gnaty (gcc)


@table @asis

@item @code{-gnaty}

Enable built-in style checks (@ref{fb,,Style Checking}).
@end table

@geindex -gnatz (gcc)


@table @asis

@item @code{-gnatz@emph{m}}

Distribution stub generation and compilation
(@code{m}=r/c for receiver/caller stubs).
@end table

@geindex -I (gcc)


@table @asis

@item @code{-I@emph{dir}}

@geindex RTL

Direct GNAT to search the @code{dir} directory for source files needed by
the current compilation
(see @ref{89,,Search Paths and the Run-Time Library (RTL)}).
@end table

@geindex -I- (gcc)


@table @asis

@item @code{-I-}

@geindex RTL

Except for the source file named in the command line, do not look for source
files in the directory containing the source file named in the command line
(see @ref{89,,Search Paths and the Run-Time Library (RTL)}).
@end table

@geindex -o (gcc)


@table @asis

@item @code{-o @emph{file}}

This switch is used in @code{gcc} to redirect the generated object file
and its associated ALI file. Beware of this switch with GNAT, because it may
cause the object file and ALI file to have different names which in turn
may confuse the binder and the linker.
@end table

@geindex -nostdinc (gcc)


@table @asis

@item @code{-nostdinc}

Inhibit the search of the default location for the GNAT Run Time
Library (RTL) source files.
@end table

@geindex -nostdlib (gcc)


@table @asis

@item @code{-nostdlib}

Inhibit the search of the default location for the GNAT Run Time
Library (RTL) ALI files.
@end table

@geindex -O (gcc)


@table @asis

@item @code{-O[@emph{n}]}

@code{n} controls the optimization level:


@multitable {xxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} 
@item

@emph{n}

@tab

Effect

@item

@emph{0}

@tab

No optimization, the default setting if no @code{-O} appears

@item

@emph{1}

@tab

Normal optimization, the default if you specify @code{-O} without an
operand. A good compromise between code quality and compilation
time.

@item

@emph{2}

@tab

Extensive optimization, may improve execution time, possibly at
the cost of substantially increased compilation time.

@item

@emph{3}

@tab

Same as @code{-O2}, and also includes inline expansion for small
subprograms in the same unit.

@item

@emph{s}

@tab

Optimize space usage

@end multitable


See also @ref{fc,,Optimization Levels}.
@end table

@geindex -pass-exit-codes (gcc)


@table @asis

@item @code{-pass-exit-codes}

Catch exit codes from the compiler and use the most meaningful as
exit status.
@end table

@geindex --RTS (gcc)


@table @asis

@item @code{--RTS=@emph{rts-path}}

Specifies the default location of the run-time library. Same meaning as the
equivalent @code{gnatmake} flag (@ref{dc,,Switches for gnatmake}).
@end table

@geindex -S (gcc)


@table @asis

@item @code{-S}

Used in place of @code{-c} to
cause the assembler source file to be
generated, using @code{.s} as the extension,
instead of the object file.
This may be useful if you need to examine the generated assembly code.
@end table

@geindex -fverbose-asm (gcc)


@table @asis

@item @code{-fverbose-asm}

Used in conjunction with @code{-S}
to cause the generated assembly code file to be annotated with variable
names, making it significantly easier to follow.
@end table

@geindex -v (gcc)


@table @asis

@item @code{-v}

Show commands generated by the @code{gcc} driver. Normally used only for
debugging purposes or if you need to be sure what version of the
compiler you are executing.
@end table

@geindex -V (gcc)


@table @asis

@item @code{-V @emph{ver}}

Execute @code{ver} version of the compiler. This is the @code{gcc}
version, not the GNAT version.
@end table

@geindex -w (gcc)


@table @asis

@item @code{-w}

Turn off warnings generated by the back end of the compiler. Use of
this switch also causes the default for front end warnings to be set
to suppress (as though @code{-gnatws} had appeared at the start of
the options).
@end table

@geindex Combining GNAT switches

You may combine a sequence of GNAT switches into a single switch. For
example, the combined switch

@quotation

@example
-gnatofi3
@end example
@end quotation

is equivalent to specifying the following sequence of switches:

@quotation

@example
-gnato -gnatf -gnati3
@end example
@end quotation

The following restrictions apply to the combination of switches
in this manner:


@itemize *

@item 
The switch @code{-gnatc} if combined with other switches must come
first in the string.

@item 
The switch @code{-gnats} if combined with other switches must come
first in the string.

@item 
The switches
@code{-gnatzc} and @code{-gnatzr} may not be combined with any other
switches, and only one of them may appear in the command line.

@item 
The switch @code{-gnat-p} may not be combined with any other switch.

@item 
Once a 'y' appears in the string (that is a use of the @code{-gnaty}
switch), then all further characters in the switch are interpreted
as style modifiers (see description of @code{-gnaty}).

@item 
Once a 'd' appears in the string (that is a use of the @code{-gnatd}
switch), then all further characters in the switch are interpreted
as debug flags (see description of @code{-gnatd}).

@item 
Once a 'w' appears in the string (that is a use of the @code{-gnatw}
switch), then all further characters in the switch are interpreted
as warning mode modifiers (see description of @code{-gnatw}).

@item 
Once a 'V' appears in the string (that is a use of the @code{-gnatV}
switch), then all further characters in the switch are interpreted
as validity checking options (@ref{f6,,Validity Checking}).

@item 
Option 'em', 'ec', 'ep', 'l=' and 'R' must be the last options in
a combined list of options.
@end itemize

@node Output and Error Message Control,Warning Message Control,Alphabetical List of All Switches,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat id14}@anchor{fd}@anchor{gnat_ugn/building_executable_programs_with_gnat output-and-error-message-control}@anchor{fe}
@subsection Output and Error Message Control


@geindex stderr

The standard default format for error messages is called 'brief format'.
Brief format messages are written to @code{stderr} (the standard error
file) and have the following form:

@example
e.adb:3:04: Incorrect spelling of keyword "function"
e.adb:4:20: ";" should be "is"
@end example

The first integer after the file name is the line number in the file,
and the second integer is the column number within the line.
@code{GPS} can parse the error messages
and point to the referenced character.
The following switches provide control over the error message
format:

@geindex -gnatv (gcc)


@table @asis

@item @code{-gnatv}

The @code{v} stands for verbose.
The effect of this setting is to write long-format error
messages to @code{stdout} (the standard output file.
The same program compiled with the
@code{-gnatv} switch would generate:

@example
3. funcion X (Q : Integer)
   |
>>> Incorrect spelling of keyword "function"
4. return Integer;
                 |
>>> ";" should be "is"
@end example

The vertical bar indicates the location of the error, and the @code{>>>}
prefix can be used to search for error messages. When this switch is
used the only source lines output are those with errors.
@end table

@geindex -gnatl (gcc)


@table @asis

@item @code{-gnatl}

The @code{l} stands for list.
This switch causes a full listing of
the file to be generated. In the case where a body is
compiled, the corresponding spec is also listed, along
with any subunits. Typical output from compiling a package
body @code{p.adb} might look like:

@example
Compiling: p.adb

     1. package body p is
     2.    procedure a;
     3.    procedure a is separate;
     4. begin
     5.    null
               |
        >>> missing ";"

     6. end;

Compiling: p.ads

     1. package p is
     2.    pragma Elaborate_Body
                                |
        >>> missing ";"

     3. end p;

Compiling: p-a.adb

     1. separate p
                |
        >>> missing "("

     2. procedure a is
     3. begin
     4.    null
               |
        >>> missing ";"

     5. end;
@end example

When you specify the @code{-gnatv} or @code{-gnatl} switches and
standard output is redirected, a brief summary is written to
@code{stderr} (standard error) giving the number of error messages and
warning messages generated.
@end table

@geindex -gnatl=fname (gcc)


@table @asis

@item @code{-gnatl=@emph{fname}}

This has the same effect as @code{-gnatl} except that the output is
written to a file instead of to standard output. If the given name
@code{fname} does not start with a period, then it is the full name
of the file to be written. If @code{fname} is an extension, it is
appended to the name of the file being compiled. For example, if
file @code{xyz.adb} is compiled with @code{-gnatl=.lst},
then the output is written to file xyz.adb.lst.
@end table

@geindex -gnatU (gcc)


@table @asis

@item @code{-gnatU}

This switch forces all error messages to be preceded by the unique
string 'error:'. This means that error messages take a few more
characters in space, but allows easy searching for and identification
of error messages.
@end table

@geindex -gnatb (gcc)


@table @asis

@item @code{-gnatb}

The @code{b} stands for brief.
This switch causes GNAT to generate the
brief format error messages to @code{stderr} (the standard error
file) as well as the verbose
format message or full listing (which as usual is written to
@code{stdout} (the standard output file).
@end table

@geindex -gnatm (gcc)


@table @asis

@item @code{-gnatm=@emph{n}}

The @code{m} stands for maximum.
@code{n} is a decimal integer in the
range of 1 to 999999 and limits the number of error or warning
messages to be generated. For example, using
@code{-gnatm2} might yield

@example
e.adb:3:04: Incorrect spelling of keyword "function"
e.adb:5:35: missing ".."
fatal error: maximum number of errors detected
compilation abandoned
@end example

The default setting if
no switch is given is 9999. If the number of warnings reaches this
limit, then a message is output and further warnings are suppressed,
but the compilation is continued. If the number of error messages
reaches this limit, then a message is output and the compilation
is abandoned. A value of zero means that no limit applies.

Note that the equal sign is optional, so the switches
@code{-gnatm2} and @code{-gnatm=2} are equivalent.
@end table

@geindex -gnatf (gcc)


@table @asis

@item @code{-gnatf}

@geindex Error messages
@geindex suppressing

The @code{f} stands for full.
Normally, the compiler suppresses error messages that are likely to be
redundant. This switch causes all error
messages to be generated. In particular, in the case of
references to undefined variables. If a given variable is referenced
several times, the normal format of messages is

@example
e.adb:7:07: "V" is undefined (more references follow)
@end example

where the parenthetical comment warns that there are additional
references to the variable @code{V}. Compiling the same program with the
@code{-gnatf} switch yields

@example
e.adb:7:07: "V" is undefined
e.adb:8:07: "V" is undefined
e.adb:8:12: "V" is undefined
e.adb:8:16: "V" is undefined
e.adb:9:07: "V" is undefined
e.adb:9:12: "V" is undefined
@end example

The @code{-gnatf} switch also generates additional information for
some error messages.  Some examples are:


@itemize *

@item 
Details on possibly non-portable unchecked conversion

@item 
List possible interpretations for ambiguous calls

@item 
Additional details on incorrect parameters
@end itemize
@end table

@geindex -gnatjnn (gcc)


@table @asis

@item @code{-gnatjnn}

In normal operation mode (or if @code{-gnatj0} is used), then error messages
with continuation lines are treated as though the continuation lines were
separate messages (and so a warning with two continuation lines counts as
three warnings, and is listed as three separate messages).

If the @code{-gnatjnn} switch is used with a positive value for nn, then
messages are output in a different manner. A message and all its continuation
lines are treated as a unit, and count as only one warning or message in the
statistics totals. Furthermore, the message is reformatted so that no line
is longer than nn characters.
@end table

@geindex -gnatq (gcc)


@table @asis

@item @code{-gnatq}

The @code{q} stands for quit (really 'don't quit').
In normal operation mode, the compiler first parses the program and
determines if there are any syntax errors. If there are, appropriate
error messages are generated and compilation is immediately terminated.
This switch tells
GNAT to continue with semantic analysis even if syntax errors have been
found. This may enable the detection of more errors in a single run. On
the other hand, the semantic analyzer is more likely to encounter some
internal fatal error when given a syntactically invalid tree.
@end table

@geindex -gnatQ (gcc)


@table @asis

@item @code{-gnatQ}

In normal operation mode, the @code{ALI} file is not generated if any
illegalities are detected in the program. The use of @code{-gnatQ} forces
generation of the @code{ALI} file. This file is marked as being in
error, so it cannot be used for binding purposes, but it does contain
reasonably complete cross-reference information, and thus may be useful
for use by tools (e.g., semantic browsing tools or integrated development
environments) that are driven from the @code{ALI} file. This switch
implies @code{-gnatq}, since the semantic phase must be run to get a
meaningful ALI file.

In addition, if @code{-gnatt} is also specified, then the tree file is
generated even if there are illegalities. It may be useful in this case
to also specify @code{-gnatq} to ensure that full semantic processing
occurs. The resulting tree file can be processed by ASIS, for the purpose
of providing partial information about illegal units, but if the error
causes the tree to be badly malformed, then ASIS may crash during the
analysis.

When @code{-gnatQ} is used and the generated @code{ALI} file is marked as
being in error, @code{gnatmake} will attempt to recompile the source when it
finds such an @code{ALI} file, including with switch @code{-gnatc}.

Note that @code{-gnatQ} has no effect if @code{-gnats} is specified,
since ALI files are never generated if @code{-gnats} is set.
@end table

@node Warning Message Control,Debugging and Assertion Control,Output and Error Message Control,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat warning-message-control}@anchor{fa}@anchor{gnat_ugn/building_executable_programs_with_gnat id15}@anchor{ff}
@subsection Warning Message Control


@geindex Warning messages

In addition to error messages, which correspond to illegalities as defined
in the Ada Reference Manual, the compiler detects two kinds of warning
situations.

First, the compiler considers some constructs suspicious and generates a
warning message to alert you to a possible error. Second, if the
compiler detects a situation that is sure to raise an exception at
run time, it generates a warning message. The following shows an example
of warning messages:

@example
e.adb:4:24: warning: creation of object may raise Storage_Error
e.adb:10:17: warning: static value out of range
e.adb:10:17: warning: "Constraint_Error" will be raised at run time
@end example

GNAT considers a large number of situations as appropriate
for the generation of warning messages. As always, warnings are not
definite indications of errors. For example, if you do an out-of-range
assignment with the deliberate intention of raising a
@code{Constraint_Error} exception, then the warning that may be
issued does not indicate an error. Some of the situations for which GNAT
issues warnings (at least some of the time) are given in the following
list. This list is not complete, and new warnings are often added to
subsequent versions of GNAT. The list is intended to give a general idea
of the kinds of warnings that are generated.


@itemize *

@item 
Possible infinitely recursive calls

@item 
Out-of-range values being assigned

@item 
Possible order of elaboration problems

@item 
Size not a multiple of alignment for a record type

@item 
Assertions (pragma Assert) that are sure to fail

@item 
Unreachable code

@item 
Address clauses with possibly unaligned values, or where an attempt is
made to overlay a smaller variable with a larger one.

@item 
Fixed-point type declarations with a null range

@item 
Direct_IO or Sequential_IO instantiated with a type that has access values

@item 
Variables that are never assigned a value

@item 
Variables that are referenced before being initialized

@item 
Task entries with no corresponding @code{accept} statement

@item 
Duplicate accepts for the same task entry in a @code{select}

@item 
Objects that take too much storage

@item 
Unchecked conversion between types of differing sizes

@item 
Missing @code{return} statement along some execution path in a function

@item 
Incorrect (unrecognized) pragmas

@item 
Incorrect external names

@item 
Allocation from empty storage pool

@item 
Potentially blocking operation in protected type

@item 
Suspicious parenthesization of expressions

@item 
Mismatching bounds in an aggregate

@item 
Attempt to return local value by reference

@item 
Premature instantiation of a generic body

@item 
Attempt to pack aliased components

@item 
Out of bounds array subscripts

@item 
Wrong length on string assignment

@item 
Violations of style rules if style checking is enabled

@item 
Unused @emph{with} clauses

@item 
@code{Bit_Order} usage that does not have any effect

@item 
@code{Standard.Duration} used to resolve universal fixed expression

@item 
Dereference of possibly null value

@item 
Declaration that is likely to cause storage error

@item 
Internal GNAT unit @emph{with}ed by application unit

@item 
Values known to be out of range at compile time

@item 
Unreferenced or unmodified variables. Note that a special
exemption applies to variables which contain any of the substrings
@code{DISCARD, DUMMY, IGNORE, JUNK, UNUSED}, in any casing. Such variables
are considered likely to be intentionally used in a situation where
otherwise a warning would be given, so warnings of this kind are
always suppressed for such variables.

@item 
Address overlays that could clobber memory

@item 
Unexpected initialization when address clause present

@item 
Bad alignment for address clause

@item 
Useless type conversions

@item 
Redundant assignment statements and other redundant constructs

@item 
Useless exception handlers

@item 
Accidental hiding of name by child unit

@item 
Access before elaboration detected at compile time

@item 
A range in a @code{for} loop that is known to be null or might be null
@end itemize

The following section lists compiler switches that are available
to control the handling of warning messages. It is also possible
to exercise much finer control over what warnings are issued and
suppressed using the GNAT pragma Warnings (see the description
of the pragma in the @cite{GNAT_Reference_manual}).

@geindex -gnatwa (gcc)


@table @asis

@item @code{-gnatwa}

@emph{Activate most optional warnings.}

This switch activates most optional warning messages.  See the remaining list
in this section for details on optional warning messages that can be
individually controlled.  The warnings that are not turned on by this
switch are:


@itemize *

@item 
@code{-gnatwd} (implicit dereferencing)

@item 
@code{-gnatw.d} (tag warnings with -gnatw switch)

@item 
@code{-gnatwh} (hiding)

@item 
@code{-gnatw.h} (holes in record layouts)

@item 
@code{-gnatw.j} (late primitives of tagged types)

@item 
@code{-gnatw.k} (redefinition of names in standard)

@item 
@code{-gnatwl} (elaboration warnings)

@item 
@code{-gnatw.l} (inherited aspects)

@item 
@code{-gnatw.n} (atomic synchronization)

@item 
@code{-gnatwo} (address clause overlay)

@item 
@code{-gnatw.o} (values set by out parameters ignored)

@item 
@code{-gnatw.q} (questionable layout of record types)

@item 
@code{-gnatw.s} (overridden size clause)

@item 
@code{-gnatwt} (tracking of deleted conditional code)

@item 
@code{-gnatw.u} (unordered enumeration)

@item 
@code{-gnatw.w} (use of Warnings Off)

@item 
@code{-gnatw.y} (reasons for package needing body)
@end itemize

All other optional warnings are turned on.
@end table

@geindex -gnatwA (gcc)


@table @asis

@item @code{-gnatwA}

@emph{Suppress all optional errors.}

This switch suppresses all optional warning messages, see remaining list
in this section for details on optional warning messages that can be
individually controlled. Note that unlike switch @code{-gnatws}, the
use of switch @code{-gnatwA} does not suppress warnings that are
normally given unconditionally and cannot be individually controlled
(for example, the warning about a missing exit path in a function).
Also, again unlike switch @code{-gnatws}, warnings suppressed by
the use of switch @code{-gnatwA} can be individually turned back
on. For example the use of switch @code{-gnatwA} followed by
switch @code{-gnatwd} will suppress all optional warnings except
the warnings for implicit dereferencing.
@end table

@geindex -gnatw.a (gcc)


@table @asis

@item @code{-gnatw.a}

@emph{Activate warnings on failing assertions.}

@geindex Assert failures

This switch activates warnings for assertions where the compiler can tell at
compile time that the assertion will fail. Note that this warning is given
even if assertions are disabled. The default is that such warnings are
generated.
@end table

@geindex -gnatw.A (gcc)


@table @asis

@item @code{-gnatw.A}

@emph{Suppress warnings on failing assertions.}

@geindex Assert failures

This switch suppresses warnings for assertions where the compiler can tell at
compile time that the assertion will fail.
@end table

@geindex -gnatwb (gcc)


@table @asis

@item @code{-gnatwb}

@emph{Activate warnings on bad fixed values.}

@geindex Bad fixed values

@geindex Fixed-point Small value

@geindex Small value

This switch activates warnings for static fixed-point expressions whose
value is not an exact multiple of Small. Such values are implementation
dependent, since an implementation is free to choose either of the multiples
that surround the value. GNAT always chooses the closer one, but this is not
required behavior, and it is better to specify a value that is an exact
multiple, ensuring predictable execution. The default is that such warnings
are not generated.
@end table

@geindex -gnatwB (gcc)


@table @asis

@item @code{-gnatwB}

@emph{Suppress warnings on bad fixed values.}

This switch suppresses warnings for static fixed-point expressions whose
value is not an exact multiple of Small.
@end table

@geindex -gnatw.b (gcc)


@table @asis

@item @code{-gnatw.b}

@emph{Activate warnings on biased representation.}

@geindex Biased representation

This switch activates warnings when a size clause, value size clause, component
clause, or component size clause forces the use of biased representation for an
integer type (e.g. representing a range of 10..11 in a single bit by using 0/1
to represent 10/11). The default is that such warnings are generated.
@end table

@geindex -gnatwB (gcc)


@table @asis

@item @code{-gnatw.B}

@emph{Suppress warnings on biased representation.}

This switch suppresses warnings for representation clauses that force the use
of biased representation.
@end table

@geindex -gnatwc (gcc)


@table @asis

@item @code{-gnatwc}

@emph{Activate warnings on conditionals.}

@geindex Conditionals
@geindex constant

This switch activates warnings for conditional expressions used in
tests that are known to be True or False at compile time. The default
is that such warnings are not generated.
Note that this warning does
not get issued for the use of boolean variables or constants whose
values are known at compile time, since this is a standard technique
for conditional compilation in Ada, and this would generate too many
false positive warnings.

This warning option also activates a special test for comparisons using
the operators '>=' and' <='.
If the compiler can tell that only the equality condition is possible,
then it will warn that the '>' or '<' part of the test
is useless and that the operator could be replaced by '='.
An example would be comparing a @code{Natural} variable <= 0.

This warning option also generates warnings if
one or both tests is optimized away in a membership test for integer
values if the result can be determined at compile time. Range tests on
enumeration types are not included, since it is common for such tests
to include an end point.

This warning can also be turned on using @code{-gnatwa}.
@end table

@geindex -gnatwC (gcc)


@table @asis

@item @code{-gnatwC}

@emph{Suppress warnings on conditionals.}

This switch suppresses warnings for conditional expressions used in
tests that are known to be True or False at compile time.
@end table

@geindex -gnatw.c (gcc)


@table @asis

@item @code{-gnatw.c}

@emph{Activate warnings on missing component clauses.}

@geindex Component clause
@geindex missing

This switch activates warnings for record components where a record
representation clause is present and has component clauses for the
majority, but not all, of the components. A warning is given for each
component for which no component clause is present.
@end table

@geindex -gnatwC (gcc)


@table @asis

@item @code{-gnatw.C}

@emph{Suppress warnings on missing component clauses.}

This switch suppresses warnings for record components that are
missing a component clause in the situation described above.
@end table

@geindex -gnatwd (gcc)


@table @asis

@item @code{-gnatwd}

@emph{Activate warnings on implicit dereferencing.}

If this switch is set, then the use of a prefix of an access type
in an indexed component, slice, or selected component without an
explicit @code{.all} will generate a warning. With this warning
enabled, access checks occur only at points where an explicit
@code{.all} appears in the source code (assuming no warnings are
generated as a result of this switch). The default is that such
warnings are not generated.
@end table

@geindex -gnatwD (gcc)


@table @asis

@item @code{-gnatwD}

@emph{Suppress warnings on implicit dereferencing.}

@geindex Implicit dereferencing

@geindex Dereferencing
@geindex implicit

This switch suppresses warnings for implicit dereferences in
indexed components, slices, and selected components.
@end table

@geindex -gnatw.d (gcc)


@table @asis

@item @code{-gnatw.d}

@emph{Activate tagging of warning and info messages.}

If this switch is set, then warning messages are tagged, with one of the
following strings:

@quotation


@itemize -

@item 
@emph{[-gnatw?]}
Used to tag warnings controlled by the switch @code{-gnatwx} where x
is a letter a-z.

@item 
@emph{[-gnatw.?]}
Used to tag warnings controlled by the switch @code{-gnatw.x} where x
is a letter a-z.

@item 
@emph{[-gnatel]}
Used to tag elaboration information (info) messages generated when the
static model of elaboration is used and the @code{-gnatel} switch is set.

@item 
@emph{[restriction warning]}
Used to tag warning messages for restriction violations, activated by use
of the pragma @code{Restriction_Warnings}.

@item 
@emph{[warning-as-error]}
Used to tag warning messages that have been converted to error messages by
use of the pragma Warning_As_Error. Note that such warnings are prefixed by
the string "error: " rather than "warning: ".

@item 
@emph{[enabled by default]}
Used to tag all other warnings that are always given by default, unless
warnings are completely suppressed using pragma @emph{Warnings(Off)} or
the switch @code{-gnatws}.
@end itemize
@end quotation
@end table

@geindex -gnatw.d (gcc)


@table @asis

@item @code{-gnatw.D}

@emph{Deactivate tagging of warning and info messages messages.}

If this switch is set, then warning messages return to the default
mode in which warnings and info messages are not tagged as described above for
@code{-gnatw.d}.
@end table

@geindex -gnatwe (gcc)

@geindex Warnings
@geindex treat as error


@table @asis

@item @code{-gnatwe}

@emph{Treat warnings and style checks as errors.}

This switch causes warning messages and style check messages to be
treated as errors.
The warning string still appears, but the warning messages are counted
as errors, and prevent the generation of an object file. Note that this
is the only -gnatw switch that affects the handling of style check messages.
Note also that this switch has no effect on info (information) messages, which
are not treated as errors if this switch is present.
@end table

@geindex -gnatw.e (gcc)


@table @asis

@item @code{-gnatw.e}

@emph{Activate every optional warning.}

@geindex Warnings
@geindex activate every optional warning

This switch activates all optional warnings, including those which
are not activated by @code{-gnatwa}. The use of this switch is not
recommended for normal use. If you turn this switch on, it is almost
certain that you will get large numbers of useless warnings. The
warnings that are excluded from @code{-gnatwa} are typically highly
specialized warnings that are suitable for use only in code that has
been specifically designed according to specialized coding rules.
@end table

@geindex -gnatwE (gcc)

@geindex Warnings
@geindex treat as error


@table @asis

@item @code{-gnatwE}

@emph{Treat all run-time exception warnings as errors.}

This switch causes warning messages regarding errors that will be raised
during run-time execution to be treated as errors.
@end table

@geindex -gnatwf (gcc)


@table @asis

@item @code{-gnatwf}

@emph{Activate warnings on unreferenced formals.}

@geindex Formals
@geindex unreferenced

This switch causes a warning to be generated if a formal parameter
is not referenced in the body of the subprogram. This warning can
also be turned on using @code{-gnatwu}. The
default is that these warnings are not generated.
@end table

@geindex -gnatwF (gcc)


@table @asis

@item @code{-gnatwF}

@emph{Suppress warnings on unreferenced formals.}

This switch suppresses warnings for unreferenced formal
parameters. Note that the
combination @code{-gnatwu} followed by @code{-gnatwF} has the
effect of warning on unreferenced entities other than subprogram
formals.
@end table

@geindex -gnatwg (gcc)


@table @asis

@item @code{-gnatwg}

@emph{Activate warnings on unrecognized pragmas.}

@geindex Pragmas
@geindex unrecognized

This switch causes a warning to be generated if an unrecognized
pragma is encountered. Apart from issuing this warning, the
pragma is ignored and has no effect. The default
is that such warnings are issued (satisfying the Ada Reference
Manual requirement that such warnings appear).
@end table

@geindex -gnatwG (gcc)


@table @asis

@item @code{-gnatwG}

@emph{Suppress warnings on unrecognized pragmas.}

This switch suppresses warnings for unrecognized pragmas.
@end table

@geindex -gnatw.g (gcc)


@table @asis

@item @code{-gnatw.g}

@emph{Warnings used for GNAT sources.}

This switch sets the warning categories that are used by the standard
GNAT style. Currently this is equivalent to
@code{-gnatwAao.q.s.CI.V.X.Z}
but more warnings may be added in the future without advanced notice.
@end table

@geindex -gnatwh (gcc)


@table @asis

@item @code{-gnatwh}

@emph{Activate warnings on hiding.}

@geindex Hiding of Declarations

This switch activates warnings on hiding declarations that are considered
potentially confusing. Not all cases of hiding cause warnings; for example an
overriding declaration hides an implicit declaration, which is just normal
code. The default is that warnings on hiding are not generated.
@end table

@geindex -gnatwH (gcc)


@table @asis

@item @code{-gnatwH}

@emph{Suppress warnings on hiding.}

This switch suppresses warnings on hiding declarations.
@end table

@geindex -gnatw.h (gcc)


@table @asis

@item @code{-gnatw.h}

@emph{Activate warnings on holes/gaps in records.}

@geindex Record Representation (gaps)

This switch activates warnings on component clauses in record
representation clauses that leave holes (gaps) in the record layout.
If this warning option is active, then record representation clauses
should specify a contiguous layout, adding unused fill fields if needed.
@end table

@geindex -gnatw.H (gcc)


@table @asis

@item @code{-gnatw.H}

@emph{Suppress warnings on holes/gaps in records.}

This switch suppresses warnings on component clauses in record
representation clauses that leave holes (haps) in the record layout.
@end table

@geindex -gnatwi (gcc)


@table @asis

@item @code{-gnatwi}

@emph{Activate warnings on implementation units.}

This switch activates warnings for a @emph{with} of an internal GNAT
implementation unit, defined as any unit from the @code{Ada},
@code{Interfaces}, @code{GNAT},
or @code{System}
hierarchies that is not
documented in either the Ada Reference Manual or the GNAT
Programmer's Reference Manual. Such units are intended only
for internal implementation purposes and should not be @emph{with}ed
by user programs. The default is that such warnings are generated
@end table

@geindex -gnatwI (gcc)


@table @asis

@item @code{-gnatwI}

@emph{Disable warnings on implementation units.}

This switch disables warnings for a @emph{with} of an internal GNAT
implementation unit.
@end table

@geindex -gnatw.i (gcc)


@table @asis

@item @code{-gnatw.i}

@emph{Activate warnings on overlapping actuals.}

This switch enables a warning on statically detectable overlapping actuals in
a subprogram call, when one of the actuals is an in-out parameter, and the
types of the actuals are not by-copy types. This warning is off by default.
@end table

@geindex -gnatw.I (gcc)


@table @asis

@item @code{-gnatw.I}

@emph{Disable warnings on overlapping actuals.}

This switch disables warnings on overlapping actuals in a call..
@end table

@geindex -gnatwj (gcc)


@table @asis

@item @code{-gnatwj}

@emph{Activate warnings on obsolescent features (Annex J).}

@geindex Features
@geindex obsolescent

@geindex Obsolescent features

If this warning option is activated, then warnings are generated for
calls to subprograms marked with @code{pragma Obsolescent} and
for use of features in Annex J of the Ada Reference Manual. In the
case of Annex J, not all features are flagged. In particular use
of the renamed packages (like @code{Text_IO}) and use of package
@code{ASCII} are not flagged, since these are very common and
would generate many annoying positive warnings. The default is that
such warnings are not generated.

In addition to the above cases, warnings are also generated for
GNAT features that have been provided in past versions but which
have been superseded (typically by features in the new Ada standard).
For example, @code{pragma Ravenscar} will be flagged since its
function is replaced by @code{pragma Profile(Ravenscar)}, and
@code{pragma Interface_Name} will be flagged since its function
is replaced by @code{pragma Import}.

Note that this warning option functions differently from the
restriction @code{No_Obsolescent_Features} in two respects.
First, the restriction applies only to annex J features.
Second, the restriction does flag uses of package @code{ASCII}.
@end table

@geindex -gnatwJ (gcc)


@table @asis

@item @code{-gnatwJ}

@emph{Suppress warnings on obsolescent features (Annex J).}

This switch disables warnings on use of obsolescent features.
@end table

@geindex -gnatw.j (gcc)


@table @asis

@item @code{-gnatw.j}

@emph{Activate warnings on late declarations of tagged type primitives.}

This switch activates warnings on visible primitives added to a
tagged type after deriving a private extension from it.
@end table

@geindex -gnatw.J (gcc)


@table @asis

@item @code{-gnatw.J}

@emph{Suppress warnings on late declarations of tagged type primitives.}

This switch suppresses warnings on visible primitives added to a
tagged type after deriving a private extension from it.
@end table

@geindex -gnatwk (gcc)


@table @asis

@item @code{-gnatwk}

@emph{Activate warnings on variables that could be constants.}

This switch activates warnings for variables that are initialized but
never modified, and then could be declared constants. The default is that
such warnings are not given.
@end table

@geindex -gnatwK (gcc)


@table @asis

@item @code{-gnatwK}

@emph{Suppress warnings on variables that could be constants.}

This switch disables warnings on variables that could be declared constants.
@end table

@geindex -gnatw.k (gcc)


@table @asis

@item @code{-gnatw.k}

@emph{Activate warnings on redefinition of names in standard.}

This switch activates warnings for declarations that declare a name that
is defined in package Standard. Such declarations can be confusing,
especially since the names in package Standard continue to be directly
visible, meaning that use visibiliy on such redeclared names does not
work as expected. Names of discriminants and components in records are
not included in this check.
@end table

@geindex -gnatwK (gcc)


@table @asis

@item @code{-gnatw.K}

@emph{Suppress warnings on redefinition of names in standard.}

This switch activates warnings for declarations that declare a name that
is defined in package Standard.
@end table

@geindex -gnatwl (gcc)


@table @asis

@item @code{-gnatwl}

@emph{Activate warnings for elaboration pragmas.}

@geindex Elaboration
@geindex warnings

This switch activates warnings for possible elaboration problems,
including suspicious use
of @code{Elaborate} pragmas, when using the static elaboration model, and
possible situations that may raise @code{Program_Error} when using the
dynamic elaboration model.
See the section in this guide on elaboration checking for further details.
The default is that such warnings
are not generated.
@end table

@geindex -gnatwL (gcc)


@table @asis

@item @code{-gnatwL}

@emph{Suppress warnings for elaboration pragmas.}

This switch suppresses warnings for possible elaboration problems.
@end table

@geindex -gnatw.l (gcc)


@table @asis

@item @code{-gnatw.l}

@emph{List inherited aspects.}

This switch causes the compiler to list inherited invariants,
preconditions, and postconditions from Type_Invariant'Class, Invariant'Class,
Pre'Class, and Post'Class aspects. Also list inherited subtype predicates.
@end table

@geindex -gnatw.L (gcc)


@table @asis

@item @code{-gnatw.L}

@emph{Suppress listing of inherited aspects.}

This switch suppresses listing of inherited aspects.
@end table

@geindex -gnatwm (gcc)


@table @asis

@item @code{-gnatwm}

@emph{Activate warnings on modified but unreferenced variables.}

This switch activates warnings for variables that are assigned (using
an initialization value or with one or more assignment statements) but
whose value is never read. The warning is suppressed for volatile
variables and also for variables that are renamings of other variables
or for which an address clause is given.
The default is that these warnings are not given.
@end table

@geindex -gnatwM (gcc)


@table @asis

@item @code{-gnatwM}

@emph{Disable warnings on modified but unreferenced variables.}

This switch disables warnings for variables that are assigned or
initialized, but never read.
@end table

@geindex -gnatw.m (gcc)


@table @asis

@item @code{-gnatw.m}

@emph{Activate warnings on suspicious modulus values.}

This switch activates warnings for modulus values that seem suspicious.
The cases caught are where the size is the same as the modulus (e.g.
a modulus of 7 with a size of 7 bits), and modulus values of 32 or 64
with no size clause. The guess in both cases is that 2**x was intended
rather than x. In addition expressions of the form 2*x for small x
generate a warning (the almost certainly accurate guess being that
2**x was intended). The default is that these warnings are given.
@end table

@geindex -gnatw.M (gcc)


@table @asis

@item @code{-gnatw.M}

@emph{Disable warnings on suspicious modulus values.}

This switch disables warnings for suspicious modulus values.
@end table

@geindex -gnatwn (gcc)


@table @asis

@item @code{-gnatwn}

@emph{Set normal warnings mode.}

This switch sets normal warning mode, in which enabled warnings are
issued and treated as warnings rather than errors. This is the default
mode. the switch @code{-gnatwn} can be used to cancel the effect of
an explicit @code{-gnatws} or
@code{-gnatwe}. It also cancels the effect of the
implicit @code{-gnatwe} that is activated by the
use of @code{-gnatg}.
@end table

@geindex -gnatw.n (gcc)

@geindex Atomic Synchronization
@geindex warnings


@table @asis

@item @code{-gnatw.n}

@emph{Activate warnings on atomic synchronization.}

This switch actives warnings when an access to an atomic variable
requires the generation of atomic synchronization code. These
warnings are off by default.
@end table

@geindex -gnatw.N (gcc)


@table @asis

@item @code{-gnatw.N}

@emph{Suppress warnings on atomic synchronization.}

@geindex Atomic Synchronization
@geindex warnings

This switch suppresses warnings when an access to an atomic variable
requires the generation of atomic synchronization code.
@end table

@geindex -gnatwo (gcc)

@geindex Address Clauses
@geindex warnings


@table @asis

@item @code{-gnatwo}

@emph{Activate warnings on address clause overlays.}

This switch activates warnings for possibly unintended initialization
effects of defining address clauses that cause one variable to overlap
another. The default is that such warnings are generated.
@end table

@geindex -gnatwO (gcc)


@table @asis

@item @code{-gnatwO}

@emph{Suppress warnings on address clause overlays.}

This switch suppresses warnings on possibly unintended initialization
effects of defining address clauses that cause one variable to overlap
another.
@end table

@geindex -gnatw.o (gcc)


@table @asis

@item @code{-gnatw.o}

@emph{Activate warnings on modified but unreferenced out parameters.}

This switch activates warnings for variables that are modified by using
them as actuals for a call to a procedure with an out mode formal, where
the resulting assigned value is never read. It is applicable in the case
where there is more than one out mode formal. If there is only one out
mode formal, the warning is issued by default (controlled by -gnatwu).
The warning is suppressed for volatile
variables and also for variables that are renamings of other variables
or for which an address clause is given.
The default is that these warnings are not given.
@end table

@geindex -gnatw.O (gcc)


@table @asis

@item @code{-gnatw.O}

@emph{Disable warnings on modified but unreferenced out parameters.}

This switch suppresses warnings for variables that are modified by using
them as actuals for a call to a procedure with an out mode formal, where
the resulting assigned value is never read.
@end table

@geindex -gnatwp (gcc)

@geindex Inlining
@geindex warnings


@table @asis

@item @code{-gnatwp}

@emph{Activate warnings on ineffective pragma Inlines.}

This switch activates warnings for failure of front end inlining
(activated by @code{-gnatN}) to inline a particular call. There are
many reasons for not being able to inline a call, including most
commonly that the call is too complex to inline. The default is
that such warnings are not given.
Warnings on ineffective inlining by the gcc back-end can be activated
separately, using the gcc switch -Winline.
@end table

@geindex -gnatwP (gcc)


@table @asis

@item @code{-gnatwP}

@emph{Suppress warnings on ineffective pragma Inlines.}

This switch suppresses warnings on ineffective pragma Inlines. If the
inlining mechanism cannot inline a call, it will simply ignore the
request silently.
@end table

@geindex -gnatw.p (gcc)

@geindex Parameter order
@geindex warnings


@table @asis

@item @code{-gnatw.p}

@emph{Activate warnings on parameter ordering.}

This switch activates warnings for cases of suspicious parameter
ordering when the list of arguments are all simple identifiers that
match the names of the formals, but are in a different order. The
warning is suppressed if any use of named parameter notation is used,
so this is the appropriate way to suppress a false positive (and
serves to emphasize that the "misordering" is deliberate). The
default is that such warnings are not given.
@end table

@geindex -gnatw.P (gcc)


@table @asis

@item @code{-gnatw.P}

@emph{Suppress warnings on parameter ordering.}

This switch suppresses warnings on cases of suspicious parameter
ordering.
@end table

@geindex -gnatwq (gcc)

@geindex Parentheses
@geindex warnings


@table @asis

@item @code{-gnatwq}

@emph{Activate warnings on questionable missing parentheses.}

This switch activates warnings for cases where parentheses are not used and
the result is potential ambiguity from a readers point of view. For example
(not a > b) when a and b are modular means ((not a) > b) and very likely the
programmer intended (not (a > b)). Similarly (-x mod 5) means (-(x mod 5)) and
quite likely ((-x) mod 5) was intended. In such situations it seems best to
follow the rule of always parenthesizing to make the association clear, and
this warning switch warns if such parentheses are not present. The default
is that these warnings are given.
@end table

@geindex -gnatwQ (gcc)


@table @asis

@item @code{-gnatwQ}

@emph{Suppress warnings on questionable missing parentheses.}

This switch suppresses warnings for cases where the association is not
clear and the use of parentheses is preferred.
@end table

@geindex -gnatw.q (gcc)

@geindex Layout
@geindex warnings


@table @asis

@item @code{-gnatw.q}

@emph{Activate warnings on questionable layout of record types.}

This switch activates warnings for cases where the default layout of
a record type, that is to say the layout of its components in textual
order of the source code, would very likely cause inefficiencies in
the code generated by the compiler, both in terms of space and speed
during execution. One warning is issued for each problematic component
without representation clause in the nonvariant part and then in each
variant recursively, if any.

The purpose of these warnings is neither to prescribe an optimal layout
nor to force the use of representation clauses, but rather to get rid of
the most blatant inefficiencies in the layout. Therefore, the default
layout is matched against the following synthetic ordered layout and
the deviations are flagged on a component-by-component basis:


@itemize *

@item 
first all components or groups of components whose length is fixed
and a multiple of the storage unit,

@item 
then the remaining components whose length is fixed and not a multiple
of the storage unit,

@item 
then the remaining components whose length doesn't depend on discriminants
(that is to say, with variable but uniform length for all objects),

@item 
then all components whose length depends on discriminants,

@item 
finally the variant part (if any),
@end itemize

for the nonvariant part and for each variant recursively, if any.

The exact wording of the warning depends on whether the compiler is allowed
to reorder the components in the record type or precluded from doing it by
means of pragma @code{No_Component_Reordering}.

The default is that these warnings are not given.
@end table

@geindex -gnatw.Q (gcc)


@table @asis

@item @code{-gnatw.Q}

@emph{Suppress warnings on questionable layout of record types.}

This switch suppresses warnings for cases where the default layout of
a record type would very likely cause inefficiencies.
@end table

@geindex -gnatwr (gcc)


@table @asis

@item @code{-gnatwr}

@emph{Activate warnings on redundant constructs.}

This switch activates warnings for redundant constructs. The following
is the current list of constructs regarded as redundant:


@itemize *

@item 
Assignment of an item to itself.

@item 
Type conversion that converts an expression to its own type.

@item 
Use of the attribute @code{Base} where @code{typ'Base} is the same
as @code{typ}.

@item 
Use of pragma @code{Pack} when all components are placed by a record
representation clause.

@item 
Exception handler containing only a reraise statement (raise with no
operand) which has no effect.

@item 
Use of the operator abs on an operand that is known at compile time
to be non-negative

@item 
Comparison of an object or (unary or binary) operation of boolean type to
an explicit True value.
@end itemize

The default is that warnings for redundant constructs are not given.
@end table

@geindex -gnatwR (gcc)


@table @asis

@item @code{-gnatwR}

@emph{Suppress warnings on redundant constructs.}

This switch suppresses warnings for redundant constructs.
@end table

@geindex -gnatw.r (gcc)


@table @asis

@item @code{-gnatw.r}

@emph{Activate warnings for object renaming function.}

This switch activates warnings for an object renaming that renames a
function call, which is equivalent to a constant declaration (as
opposed to renaming the function itself).  The default is that these
warnings are given.
@end table

@geindex -gnatwT (gcc)


@table @asis

@item @code{-gnatw.R}

@emph{Suppress warnings for object renaming function.}

This switch suppresses warnings for object renaming function.
@end table

@geindex -gnatws (gcc)


@table @asis

@item @code{-gnatws}

@emph{Suppress all warnings.}

This switch completely suppresses the
output of all warning messages from the GNAT front end, including
both warnings that can be controlled by switches described in this
section, and those that are normally given unconditionally. The
effect of this suppress action can only be cancelled by a subsequent
use of the switch @code{-gnatwn}.

Note that switch @code{-gnatws} does not suppress
warnings from the @code{gcc} back end.
To suppress these back end warnings as well, use the switch @code{-w}
in addition to @code{-gnatws}. Also this switch has no effect on the
handling of style check messages.
@end table

@geindex -gnatw.s (gcc)

@geindex Record Representation (component sizes)


@table @asis

@item @code{-gnatw.s}

@emph{Activate warnings on overridden size clauses.}

This switch activates warnings on component clauses in record
representation clauses where the length given overrides that
specified by an explicit size clause for the component type. A
warning is similarly given in the array case if a specified
component size overrides an explicit size clause for the array
component type.
@end table

@geindex -gnatw.S (gcc)


@table @asis

@item @code{-gnatw.S}

@emph{Suppress warnings on overridden size clauses.}

This switch suppresses warnings on component clauses in record
representation clauses that override size clauses, and similar
warnings when an array component size overrides a size clause.
@end table

@geindex -gnatwt (gcc)

@geindex Deactivated code
@geindex warnings

@geindex Deleted code
@geindex warnings


@table @asis

@item @code{-gnatwt}

@emph{Activate warnings for tracking of deleted conditional code.}

This switch activates warnings for tracking of code in conditionals (IF and
CASE statements) that is detected to be dead code which cannot be executed, and
which is removed by the front end. This warning is off by default. This may be
useful for detecting deactivated code in certified applications.
@end table

@geindex -gnatwT (gcc)


@table @asis

@item @code{-gnatwT}

@emph{Suppress warnings for tracking of deleted conditional code.}

This switch suppresses warnings for tracking of deleted conditional code.
@end table

@geindex -gnatw.t (gcc)


@table @asis

@item @code{-gnatw.t}

@emph{Activate warnings on suspicious contracts.}

This switch activates warnings on suspicious contracts. This includes
warnings on suspicious postconditions (whether a pragma @code{Postcondition} or a
@code{Post} aspect in Ada 2012) and suspicious contract cases (pragma or aspect
@code{Contract_Cases}). A function postcondition or contract case is suspicious
when no postcondition or contract case for this function mentions the result
of the function.  A procedure postcondition or contract case is suspicious
when it only refers to the pre-state of the procedure, because in that case
it should rather be expressed as a precondition. This switch also controls
warnings on suspicious cases of expressions typically found in contracts like
quantified expressions and uses of Update attribute. The default is that such
warnings are generated.
@end table

@geindex -gnatw.T (gcc)


@table @asis

@item @code{-gnatw.T}

@emph{Suppress warnings on suspicious contracts.}

This switch suppresses warnings on suspicious contracts.
@end table

@geindex -gnatwu (gcc)


@table @asis

@item @code{-gnatwu}

@emph{Activate warnings on unused entities.}

This switch activates warnings to be generated for entities that
are declared but not referenced, and for units that are @emph{with}ed
and not
referenced. In the case of packages, a warning is also generated if
no entities in the package are referenced. This means that if a with'ed
package is referenced but the only references are in @code{use}
clauses or @code{renames}
declarations, a warning is still generated. A warning is also generated
for a generic package that is @emph{with}ed but never instantiated.
In the case where a package or subprogram body is compiled, and there
is a @emph{with} on the corresponding spec
that is only referenced in the body,
a warning is also generated, noting that the
@emph{with} can be moved to the body. The default is that
such warnings are not generated.
This switch also activates warnings on unreferenced formals
(it includes the effect of @code{-gnatwf}).
@end table

@geindex -gnatwU (gcc)


@table @asis

@item @code{-gnatwU}

@emph{Suppress warnings on unused entities.}

This switch suppresses warnings for unused entities and packages.
It also turns off warnings on unreferenced formals (and thus includes
the effect of @code{-gnatwF}).
@end table

@geindex -gnatw.u (gcc)


@table @asis

@item @code{-gnatw.u}

@emph{Activate warnings on unordered enumeration types.}

This switch causes enumeration types to be considered as conceptually
unordered, unless an explicit pragma @code{Ordered} is given for the type.
The effect is to generate warnings in clients that use explicit comparisons
or subranges, since these constructs both treat objects of the type as
ordered. (A @emph{client} is defined as a unit that is other than the unit in
which the type is declared, or its body or subunits.) Please refer to
the description of pragma @code{Ordered} in the
@cite{GNAT Reference Manual} for further details.
The default is that such warnings are not generated.
@end table

@geindex -gnatw.U (gcc)


@table @asis

@item @code{-gnatw.U}

@emph{Deactivate warnings on unordered enumeration types.}

This switch causes all enumeration types to be considered as ordered, so
that no warnings are given for comparisons or subranges for any type.
@end table

@geindex -gnatwv (gcc)

@geindex Unassigned variable warnings


@table @asis

@item @code{-gnatwv}

@emph{Activate warnings on unassigned variables.}

This switch activates warnings for access to variables which
may not be properly initialized. The default is that
such warnings are generated.
@end table

@geindex -gnatwV (gcc)


@table @asis

@item @code{-gnatwV}

@emph{Suppress warnings on unassigned variables.}

This switch suppresses warnings for access to variables which
may not be properly initialized.
For variables of a composite type, the warning can also be suppressed in
Ada 2005 by using a default initialization with a box. For example, if
Table is an array of records whose components are only partially uninitialized,
then the following code:

@example
Tab : Table := (others => <>);
@end example

will suppress warnings on subsequent statements that access components
of variable Tab.
@end table

@geindex -gnatw.v (gcc)

@geindex bit order warnings


@table @asis

@item @code{-gnatw.v}

@emph{Activate info messages for non-default bit order.}

This switch activates messages (labeled "info", they are not warnings,
just informational messages) about the effects of non-default bit-order
on records to which a component clause is applied. The effect of specifying
non-default bit ordering is a bit subtle (and changed with Ada 2005), so
these messages, which are given by default, are useful in understanding the
exact consequences of using this feature.
@end table

@geindex -gnatw.V (gcc)


@table @asis

@item @code{-gnatw.V}

@emph{Suppress info messages for non-default bit order.}

This switch suppresses information messages for the effects of specifying
non-default bit order on record components with component clauses.
@end table

@geindex -gnatww (gcc)

@geindex String indexing warnings


@table @asis

@item @code{-gnatww}

@emph{Activate warnings on wrong low bound assumption.}

This switch activates warnings for indexing an unconstrained string parameter
with a literal or S'Length. This is a case where the code is assuming that the
low bound is one, which is in general not true (for example when a slice is
passed). The default is that such warnings are generated.
@end table

@geindex -gnatwW (gcc)


@table @asis

@item @code{-gnatwW}

@emph{Suppress warnings on wrong low bound assumption.}

This switch suppresses warnings for indexing an unconstrained string parameter
with a literal or S'Length. Note that this warning can also be suppressed
in a particular case by adding an assertion that the lower bound is 1,
as shown in the following example:

@example
procedure K (S : String) is
   pragma Assert (S'First = 1);
   ...
@end example
@end table

@geindex -gnatw.w (gcc)

@geindex Warnings Off control


@table @asis

@item @code{-gnatw.w}

@emph{Activate warnings on Warnings Off pragmas.}

This switch activates warnings for use of @code{pragma Warnings (Off, entity)}
where either the pragma is entirely useless (because it suppresses no
warnings), or it could be replaced by @code{pragma Unreferenced} or
@code{pragma Unmodified}.
Also activates warnings for the case of
Warnings (Off, String), where either there is no matching
Warnings (On, String), or the Warnings (Off) did not suppress any warning.
The default is that these warnings are not given.
@end table

@geindex -gnatw.W (gcc)


@table @asis

@item @code{-gnatw.W}

@emph{Suppress warnings on unnecessary Warnings Off pragmas.}

This switch suppresses warnings for use of @code{pragma Warnings (Off, ...)}.
@end table

@geindex -gnatwx (gcc)

@geindex Export/Import pragma warnings


@table @asis

@item @code{-gnatwx}

@emph{Activate warnings on Export/Import pragmas.}

This switch activates warnings on Export/Import pragmas when
the compiler detects a possible conflict between the Ada and
foreign language calling sequences. For example, the use of
default parameters in a convention C procedure is dubious
because the C compiler cannot supply the proper default, so
a warning is issued. The default is that such warnings are
generated.
@end table

@geindex -gnatwX (gcc)


@table @asis

@item @code{-gnatwX}

@emph{Suppress warnings on Export/Import pragmas.}

This switch suppresses warnings on Export/Import pragmas.
The sense of this is that you are telling the compiler that
you know what you are doing in writing the pragma, and it
should not complain at you.
@end table

@geindex -gnatwm (gcc)


@table @asis

@item @code{-gnatw.x}

@emph{Activate warnings for No_Exception_Propagation mode.}

This switch activates warnings for exception usage when pragma Restrictions
(No_Exception_Propagation) is in effect. Warnings are given for implicit or
explicit exception raises which are not covered by a local handler, and for
exception handlers which do not cover a local raise. The default is that
these warnings are given for units that contain exception handlers.

@item @code{-gnatw.X}

@emph{Disable warnings for No_Exception_Propagation mode.}

This switch disables warnings for exception usage when pragma Restrictions
(No_Exception_Propagation) is in effect.
@end table

@geindex -gnatwy (gcc)

@geindex Ada compatibility issues warnings


@table @asis

@item @code{-gnatwy}

@emph{Activate warnings for Ada compatibility issues.}

For the most part, newer versions of Ada are upwards compatible
with older versions. For example, Ada 2005 programs will almost
always work when compiled as Ada 2012.
However there are some exceptions (for example the fact that
@code{some} is now a reserved word in Ada 2012). This
switch activates several warnings to help in identifying
and correcting such incompatibilities. The default is that
these warnings are generated. Note that at one point Ada 2005
was called Ada 0Y, hence the choice of character.
@end table

@geindex -gnatwY (gcc)

@geindex Ada compatibility issues warnings


@table @asis

@item @code{-gnatwY}

@emph{Disable warnings for Ada compatibility issues.}

This switch suppresses the warnings intended to help in identifying
incompatibilities between Ada language versions.
@end table

@geindex -gnatw.y (gcc)

@geindex Package spec needing body


@table @asis

@item @code{-gnatw.y}

@emph{Activate information messages for why package spec needs body.}

There are a number of cases in which a package spec needs a body.
For example, the use of pragma Elaborate_Body, or the declaration
of a procedure specification requiring a completion. This switch
causes information messages to be output showing why a package
specification requires a body. This can be useful in the case of
a large package specification which is unexpectedly requiring a
body. The default is that such information messages are not output.
@end table

@geindex -gnatw.Y (gcc)

@geindex No information messages for why package spec needs body


@table @asis

@item @code{-gnatw.Y}

@emph{Disable information messages for why package spec needs body.}

This switch suppresses the output of information messages showing why
a package specification needs a body.
@end table

@geindex -gnatwz (gcc)

@geindex Unchecked_Conversion warnings


@table @asis

@item @code{-gnatwz}

@emph{Activate warnings on unchecked conversions.}

This switch activates warnings for unchecked conversions
where the types are known at compile time to have different
sizes. The default is that such warnings are generated. Warnings are also
generated for subprogram pointers with different conventions.
@end table

@geindex -gnatwZ (gcc)


@table @asis

@item @code{-gnatwZ}

@emph{Suppress warnings on unchecked conversions.}

This switch suppresses warnings for unchecked conversions
where the types are known at compile time to have different
sizes or conventions.
@end table

@geindex -gnatw.z (gcc)

@geindex Size/Alignment warnings


@table @asis

@item @code{-gnatw.z}

@emph{Activate warnings for size not a multiple of alignment.}

This switch activates warnings for cases of record types with
specified @code{Size} and @code{Alignment} attributes where the
size is not a multiple of the alignment, resulting in an object
size that is greater than the specified size. The default
is that such warnings are generated.
@end table

@geindex -gnatw.Z (gcc)

@geindex Size/Alignment warnings


@table @asis

@item @code{-gnatw.Z}

@emph{Suppress warnings for size not a multiple of alignment.}

This switch suppresses warnings for cases of record types with
specified @code{Size} and @code{Alignment} attributes where the
size is not a multiple of the alignment, resulting in an object
size that is greater than the specified size.
The warning can also be
suppressed by giving an explicit @code{Object_Size} value.
@end table

@geindex -Wunused (gcc)


@table @asis

@item @code{-Wunused}

The warnings controlled by the @code{-gnatw} switch are generated by
the front end of the compiler. The GCC back end can provide
additional warnings and they are controlled by the @code{-W} switch.
For example, @code{-Wunused} activates back end
warnings for entities that are declared but not referenced.
@end table

@geindex -Wuninitialized (gcc)


@table @asis

@item @code{-Wuninitialized}

Similarly, @code{-Wuninitialized} activates
the back end warning for uninitialized variables. This switch must be
used in conjunction with an optimization level greater than zero.
@end table

@geindex -Wstack-usage (gcc)


@table @asis

@item @code{-Wstack-usage=@emph{len}}

Warn if the stack usage of a subprogram might be larger than @code{len} bytes.
See @ref{f5,,Static Stack Usage Analysis} for details.
@end table

@geindex -Wall (gcc)


@table @asis

@item @code{-Wall}

This switch enables most warnings from the GCC back end.
The code generator detects a number of warning situations that are missed
by the GNAT front end, and this switch can be used to activate them.
The use of this switch also sets the default front end warning mode to
@code{-gnatwa}, that is, most front end warnings activated as well.
@end table

@geindex -w (gcc)


@table @asis

@item @code{-w}

Conversely, this switch suppresses warnings from the GCC back end.
The use of this switch also sets the default front end warning mode to
@code{-gnatws}, that is, front end warnings suppressed as well.
@end table

@geindex -Werror (gcc)


@table @asis

@item @code{-Werror}

This switch causes warnings from the GCC back end to be treated as
errors.  The warning string still appears, but the warning messages are
counted as errors, and prevent the generation of an object file.
@end table

A string of warning parameters can be used in the same parameter. For example:

@example
-gnatwaGe
@end example

will turn on all optional warnings except for unrecognized pragma warnings,
and also specify that warnings should be treated as errors.

When no switch @code{-gnatw} is used, this is equivalent to:

@quotation


@itemize *

@item 
@code{-gnatw.a}

@item 
@code{-gnatwB}

@item 
@code{-gnatw.b}

@item 
@code{-gnatwC}

@item 
@code{-gnatw.C}

@item 
@code{-gnatwD}

@item 
@code{-gnatw.D}

@item 
@code{-gnatwF}

@item 
@code{-gnatw.F}

@item 
@code{-gnatwg}

@item 
@code{-gnatwH}

@item 
@code{-gnatw.H}

@item 
@code{-gnatwi}

@item 
@code{-gnatwJ}

@item 
@code{-gnatw.J}

@item 
@code{-gnatwK}

@item 
@code{-gnatw.K}

@item 
@code{-gnatwL}

@item 
@code{-gnatw.L}

@item 
@code{-gnatwM}

@item 
@code{-gnatw.m}

@item 
@code{-gnatwn}

@item 
@code{-gnatw.N}

@item 
@code{-gnatwo}

@item 
@code{-gnatw.O}

@item 
@code{-gnatwP}

@item 
@code{-gnatw.P}

@item 
@code{-gnatwq}

@item 
@code{-gnatw.Q}

@item 
@code{-gnatwR}

@item 
@code{-gnatw.R}

@item 
@code{-gnatw.S}

@item 
@code{-gnatwT}

@item 
@code{-gnatw.t}

@item 
@code{-gnatwU}

@item 
@code{-gnatw.U}

@item 
@code{-gnatwv}

@item 
@code{-gnatw.v}

@item 
@code{-gnatww}

@item 
@code{-gnatw.W}

@item 
@code{-gnatwx}

@item 
@code{-gnatw.X}

@item 
@code{-gnatwy}

@item 
@code{-gnatw.Y}

@item 
@code{-gnatwz}

@item 
@code{-gnatw.z}
@end itemize
@end quotation

@node Debugging and Assertion Control,Validity Checking,Warning Message Control,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat debugging-and-assertion-control}@anchor{100}@anchor{gnat_ugn/building_executable_programs_with_gnat id16}@anchor{101}
@subsection Debugging and Assertion Control


@geindex -gnata (gcc)


@table @asis

@item @code{-gnata}

@geindex Assert

@geindex Debug

@geindex Assertions

@geindex Precondition

@geindex Postcondition

@geindex Type invariants

@geindex Subtype predicates

The @code{-gnata} option is equivalent to the following @code{Assertion_Policy} pragma:

@example
pragma Assertion_Policy (Check);
@end example

Which is a shorthand for:

@example
pragma Assertion_Policy
  (Assert               => Check,
   Static_Predicate     => Check,
   Dynamic_Predicate    => Check,
   Pre                  => Check,
   Pre'Class            => Check,
   Post                 => Check,
   Post'Class           => Check,
   Type_Invariant       => Check,
   Type_Invariant'Class => Check);
@end example

The pragmas @code{Assert} and @code{Debug} normally have no effect and
are ignored. This switch, where @code{a} stands for 'assert', causes
pragmas @code{Assert} and @code{Debug} to be activated. This switch also
causes preconditions, postconditions, subtype predicates, and
type invariants to be activated.

The pragmas have the form:

@example
pragma Assert (<Boolean-expression> [, <static-string-expression>])
pragma Debug (<procedure call>)
pragma Type_Invariant (<type-local-name>, <Boolean-expression>)
pragma Predicate (<type-local-name>, <Boolean-expression>)
pragma Precondition (<Boolean-expression>, <string-expression>)
pragma Postcondition (<Boolean-expression>, <string-expression>)
@end example

The aspects have the form:

@example
with [Pre|Post|Type_Invariant|Dynamic_Predicate|Static_Predicate]
  => <Boolean-expression>;
@end example

The @code{Assert} pragma causes @code{Boolean-expression} to be tested.
If the result is @code{True}, the pragma has no effect (other than
possible side effects from evaluating the expression). If the result is
@code{False}, the exception @code{Assert_Failure} declared in the package
@code{System.Assertions} is raised (passing @code{static-string-expression}, if
present, as the message associated with the exception). If no string
expression is given, the default is a string containing the file name and
line number of the pragma.

The @code{Debug} pragma causes @code{procedure} to be called. Note that
@code{pragma Debug} may appear within a declaration sequence, allowing
debugging procedures to be called between declarations.

For the aspect specification, the @code{Boolean-expression} is evaluated.
If the result is @code{True}, the aspect has no effect. If the result
is @code{False}, the exception @code{Assert_Failure} is raised.
@end table

@node Validity Checking,Style Checking,Debugging and Assertion Control,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat validity-checking}@anchor{f6}@anchor{gnat_ugn/building_executable_programs_with_gnat id17}@anchor{102}
@subsection Validity Checking


@geindex Validity Checking

The Ada Reference Manual defines the concept of invalid values (see
RM 13.9.1). The primary source of invalid values is uninitialized
variables. A scalar variable that is left uninitialized may contain
an invalid value; the concept of invalid does not apply to access or
composite types.

It is an error to read an invalid value, but the RM does not require
run-time checks to detect such errors, except for some minimal
checking to prevent erroneous execution (i.e. unpredictable
behavior). This corresponds to the @code{-gnatVd} switch below,
which is the default. For example, by default, if the expression of a
case statement is invalid, it will raise Constraint_Error rather than
causing a wild jump, and if an array index on the left-hand side of an
assignment is invalid, it will raise Constraint_Error rather than
overwriting an arbitrary memory location.

The @code{-gnatVa} may be used to enable additional validity checks,
which are not required by the RM. These checks are often very
expensive (which is why the RM does not require them). These checks
are useful in tracking down uninitialized variables, but they are
not usually recommended for production builds, and in particular
we do not recommend using these extra validity checking options in
combination with optimization, since this can confuse the optimizer.
If performance is a consideration, leading to the need to optimize,
then the validity checking options should not be used.

The other @code{-gnatV@emph{x}} switches below allow finer-grained
control; you can enable whichever validity checks you desire. However,
for most debugging purposes, @code{-gnatVa} is sufficient, and the
default @code{-gnatVd} (i.e. standard Ada behavior) is usually
sufficient for non-debugging use.

The @code{-gnatB} switch tells the compiler to assume that all
values are valid (that is, within their declared subtype range)
except in the context of a use of the Valid attribute. This means
the compiler can generate more efficient code, since the range
of values is better known at compile time. However, an uninitialized
variable can cause wild jumps and memory corruption in this mode.

The @code{-gnatV@emph{x}} switch allows control over the validity
checking mode as described below.
The @code{x} argument is a string of letters that
indicate validity checks that are performed or not performed in addition
to the default checks required by Ada as described above.

@geindex -gnatVa (gcc)


@table @asis

@item @code{-gnatVa}

@emph{All validity checks.}

All validity checks are turned on.
That is, @code{-gnatVa} is
equivalent to @code{gnatVcdfimorst}.
@end table

@geindex -gnatVc (gcc)


@table @asis

@item @code{-gnatVc}

@emph{Validity checks for copies.}

The right hand side of assignments, and the initializing values of
object declarations are validity checked.
@end table

@geindex -gnatVd (gcc)


@table @asis

@item @code{-gnatVd}

@emph{Default (RM) validity checks.}

Some validity checks are done by default following normal Ada semantics
(RM 13.9.1 (9-11)).
A check is done in case statements that the expression is within the range
of the subtype. If it is not, Constraint_Error is raised.
For assignments to array components, a check is done that the expression used
as index is within the range. If it is not, Constraint_Error is raised.
Both these validity checks may be turned off using switch @code{-gnatVD}.
They are turned on by default. If @code{-gnatVD} is specified, a subsequent
switch @code{-gnatVd} will leave the checks turned on.
Switch @code{-gnatVD} should be used only if you are sure that all such
expressions have valid values. If you use this switch and invalid values
are present, then the program is erroneous, and wild jumps or memory
overwriting may occur.
@end table

@geindex -gnatVe (gcc)


@table @asis

@item @code{-gnatVe}

@emph{Validity checks for elementary components.}

In the absence of this switch, assignments to record or array components are
not validity checked, even if validity checks for assignments generally
(@code{-gnatVc}) are turned on. In Ada, assignment of composite values do not
require valid data, but assignment of individual components does. So for
example, there is a difference between copying the elements of an array with a
slice assignment, compared to assigning element by element in a loop. This
switch allows you to turn off validity checking for components, even when they
are assigned component by component.
@end table

@geindex -gnatVf (gcc)


@table @asis

@item @code{-gnatVf}

@emph{Validity checks for floating-point values.}

In the absence of this switch, validity checking occurs only for discrete
values. If @code{-gnatVf} is specified, then validity checking also applies
for floating-point values, and NaNs and infinities are considered invalid,
as well as out of range values for constrained types. Note that this means
that standard IEEE infinity mode is not allowed. The exact contexts
in which floating-point values are checked depends on the setting of other
options. For example, @code{-gnatVif} or @code{-gnatVfi}
(the order does not matter) specifies that floating-point parameters of mode
@code{in} should be validity checked.
@end table

@geindex -gnatVi (gcc)


@table @asis

@item @code{-gnatVi}

@emph{Validity checks for `@w{`}in`@w{`} mode parameters.}

Arguments for parameters of mode @code{in} are validity checked in function
and procedure calls at the point of call.
@end table

@geindex -gnatVm (gcc)


@table @asis

@item @code{-gnatVm}

@emph{Validity checks for `@w{`}in out`@w{`} mode parameters.}

Arguments for parameters of mode @code{in out} are validity checked in
procedure calls at the point of call. The @code{'m'} here stands for
modify, since this concerns parameters that can be modified by the call.
Note that there is no specific option to test @code{out} parameters,
but any reference within the subprogram will be tested in the usual
manner, and if an invalid value is copied back, any reference to it
will be subject to validity checking.
@end table

@geindex -gnatVn (gcc)


@table @asis

@item @code{-gnatVn}

@emph{No validity checks.}

This switch turns off all validity checking, including the default checking
for case statements and left hand side subscripts. Note that the use of
the switch @code{-gnatp} suppresses all run-time checks, including
validity checks, and thus implies @code{-gnatVn}. When this switch
is used, it cancels any other @code{-gnatV} previously issued.
@end table

@geindex -gnatVo (gcc)


@table @asis

@item @code{-gnatVo}

@emph{Validity checks for operator and attribute operands.}

Arguments for predefined operators and attributes are validity checked.
This includes all operators in package @code{Standard},
the shift operators defined as intrinsic in package @code{Interfaces}
and operands for attributes such as @code{Pos}. Checks are also made
on individual component values for composite comparisons, and on the
expressions in type conversions and qualified expressions. Checks are
also made on explicit ranges using @code{..} (e.g., slices, loops etc).
@end table

@geindex -gnatVp (gcc)


@table @asis

@item @code{-gnatVp}

@emph{Validity checks for parameters.}

This controls the treatment of parameters within a subprogram (as opposed
to @code{-gnatVi} and @code{-gnatVm} which control validity testing
of parameters on a call. If either of these call options is used, then
normally an assumption is made within a subprogram that the input arguments
have been validity checking at the point of call, and do not need checking
again within a subprogram). If @code{-gnatVp} is set, then this assumption
is not made, and parameters are not assumed to be valid, so their validity
will be checked (or rechecked) within the subprogram.
@end table

@geindex -gnatVr (gcc)


@table @asis

@item @code{-gnatVr}

@emph{Validity checks for function returns.}

The expression in @code{return} statements in functions is validity
checked.
@end table

@geindex -gnatVs (gcc)


@table @asis

@item @code{-gnatVs}

@emph{Validity checks for subscripts.}

All subscripts expressions are checked for validity, whether they appear
on the right side or left side (in default mode only left side subscripts
are validity checked).
@end table

@geindex -gnatVt (gcc)


@table @asis

@item @code{-gnatVt}

@emph{Validity checks for tests.}

Expressions used as conditions in @code{if}, @code{while} or @code{exit}
statements are checked, as well as guard expressions in entry calls.
@end table

The @code{-gnatV} switch may be followed by a string of letters
to turn on a series of validity checking options.
For example, @code{-gnatVcr}
specifies that in addition to the default validity checking, copies and
function return expressions are to be validity checked.
In order to make it easier to specify the desired combination of effects,
the upper case letters @code{CDFIMORST} may
be used to turn off the corresponding lower case option.
Thus @code{-gnatVaM} turns on all validity checking options except for
checking of @code{in out} parameters.

The specification of additional validity checking generates extra code (and
in the case of @code{-gnatVa} the code expansion can be substantial).
However, these additional checks can be very useful in detecting
uninitialized variables, incorrect use of unchecked conversion, and other
errors leading to invalid values. The use of pragma @code{Initialize_Scalars}
is useful in conjunction with the extra validity checking, since this
ensures that wherever possible uninitialized variables have invalid values.

See also the pragma @code{Validity_Checks} which allows modification of
the validity checking mode at the program source level, and also allows for
temporary disabling of validity checks.

@node Style Checking,Run-Time Checks,Validity Checking,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat id18}@anchor{103}@anchor{gnat_ugn/building_executable_programs_with_gnat style-checking}@anchor{fb}
@subsection Style Checking


@geindex Style checking

@geindex -gnaty (gcc)

The @code{-gnatyx} switch causes the compiler to
enforce specified style rules. A limited set of style rules has been used
in writing the GNAT sources themselves. This switch allows user programs
to activate all or some of these checks. If the source program fails a
specified style check, an appropriate message is given, preceded by
the character sequence '(style)'. This message does not prevent
successful compilation (unless the @code{-gnatwe} switch is used).

Note that this is by no means intended to be a general facility for
checking arbitrary coding standards. It is simply an embedding of the
style rules we have chosen for the GNAT sources. If you are starting
a project which does not have established style standards, you may
find it useful to adopt the entire set of GNAT coding standards, or
some subset of them.


The string @code{x} is a sequence of letters or digits
indicating the particular style
checks to be performed. The following checks are defined:

@geindex -gnaty[0-9] (gcc)


@table @asis

@item @code{-gnaty0}

@emph{Specify indentation level.}

If a digit from 1-9 appears
in the string after @code{-gnaty}
then proper indentation is checked, with the digit indicating the
indentation level required. A value of zero turns off this style check.
The general style of required indentation is as specified by
the examples in the Ada Reference Manual. Full line comments must be
aligned with the @code{--} starting on a column that is a multiple of
the alignment level, or they may be aligned the same way as the following
non-blank line (this is useful when full line comments appear in the middle
of a statement, or they may be aligned with the source line on the previous
non-blank line.
@end table

@geindex -gnatya (gcc)


@table @asis

@item @code{-gnatya}

@emph{Check attribute casing.}

Attribute names, including the case of keywords such as @code{digits}
used as attributes names, must be written in mixed case, that is, the
initial letter and any letter following an underscore must be uppercase.
All other letters must be lowercase.
@end table

@geindex -gnatyA (gcc)


@table @asis

@item @code{-gnatyA}

@emph{Use of array index numbers in array attributes.}

When using the array attributes First, Last, Range,
or Length, the index number must be omitted for one-dimensional arrays
and is required for multi-dimensional arrays.
@end table

@geindex -gnatyb (gcc)


@table @asis

@item @code{-gnatyb}

@emph{Blanks not allowed at statement end.}

Trailing blanks are not allowed at the end of statements. The purpose of this
rule, together with h (no horizontal tabs), is to enforce a canonical format
for the use of blanks to separate source tokens.
@end table

@geindex -gnatyB (gcc)


@table @asis

@item @code{-gnatyB}

@emph{Check Boolean operators.}

The use of AND/OR operators is not permitted except in the cases of modular
operands, array operands, and simple stand-alone boolean variables or
boolean constants. In all other cases @code{and then}/@cite{or else} are
required.
@end table

@geindex -gnatyc (gcc)


@table @asis

@item @code{-gnatyc}

@emph{Check comments, double space.}

Comments must meet the following set of rules:


@itemize *

@item 
The @code{--} that starts the column must either start in column one,
or else at least one blank must precede this sequence.

@item 
Comments that follow other tokens on a line must have at least one blank
following the @code{--} at the start of the comment.

@item 
Full line comments must have at least two blanks following the
@code{--} that starts the comment, with the following exceptions.

@item 
A line consisting only of the @code{--} characters, possibly preceded
by blanks is permitted.

@item 
A comment starting with @code{--x} where @code{x} is a special character
is permitted.
This allows proper processing of the output from specialized tools
such as @code{gnatprep} (where @code{--!} is used) and in earlier versions of the SPARK
annotation
language (where @code{--#} is used). For the purposes of this rule, a
special character is defined as being in one of the ASCII ranges
@code{16#21#...16#2F#} or @code{16#3A#...16#3F#}.
Note that this usage is not permitted
in GNAT implementation units (i.e., when @code{-gnatg} is used).

@item 
A line consisting entirely of minus signs, possibly preceded by blanks, is
permitted. This allows the construction of box comments where lines of minus
signs are used to form the top and bottom of the box.

@item 
A comment that starts and ends with @code{--} is permitted as long as at
least one blank follows the initial @code{--}. Together with the preceding
rule, this allows the construction of box comments, as shown in the following
example:

@example
---------------------------
-- This is a box comment --
-- with two text lines.  --
---------------------------
@end example
@end itemize
@end table

@geindex -gnatyC (gcc)


@table @asis

@item @code{-gnatyC}

@emph{Check comments, single space.}

This is identical to @code{c} except that only one space
is required following the @code{--} of a comment instead of two.
@end table

@geindex -gnatyd (gcc)


@table @asis

@item @code{-gnatyd}

@emph{Check no DOS line terminators present.}

All lines must be terminated by a single ASCII.LF
character (in particular the DOS line terminator sequence CR/LF is not
allowed).
@end table

@geindex -gnatye (gcc)


@table @asis

@item @code{-gnatye}

@emph{Check end/exit labels.}

Optional labels on @code{end} statements ending subprograms and on
@code{exit} statements exiting named loops, are required to be present.
@end table

@geindex -gnatyf (gcc)


@table @asis

@item @code{-gnatyf}

@emph{No form feeds or vertical tabs.}

Neither form feeds nor vertical tab characters are permitted
in the source text.
@end table

@geindex -gnatyg (gcc)


@table @asis

@item @code{-gnatyg}

@emph{GNAT style mode.}

The set of style check switches is set to match that used by the GNAT sources.
This may be useful when developing code that is eventually intended to be
incorporated into GNAT. Currently this is equivalent to @code{-gnatwydISux})
but additional style switches may be added to this set in the future without
advance notice.
@end table

@geindex -gnatyh (gcc)


@table @asis

@item @code{-gnatyh}

@emph{No horizontal tabs.}

Horizontal tab characters are not permitted in the source text.
Together with the b (no blanks at end of line) check, this
enforces a canonical form for the use of blanks to separate
source tokens.
@end table

@geindex -gnatyi (gcc)


@table @asis

@item @code{-gnatyi}

@emph{Check if-then layout.}

The keyword @code{then} must appear either on the same
line as corresponding @code{if}, or on a line on its own, lined
up under the @code{if}.
@end table

@geindex -gnatyI (gcc)


@table @asis

@item @code{-gnatyI}

@emph{check mode IN keywords.}

Mode @code{in} (the default mode) is not
allowed to be given explicitly. @code{in out} is fine,
but not @code{in} on its own.
@end table

@geindex -gnatyk (gcc)


@table @asis

@item @code{-gnatyk}

@emph{Check keyword casing.}

All keywords must be in lower case (with the exception of keywords
such as @code{digits} used as attribute names to which this check
does not apply).
@end table

@geindex -gnatyl (gcc)


@table @asis

@item @code{-gnatyl}

@emph{Check layout.}

Layout of statement and declaration constructs must follow the
recommendations in the Ada Reference Manual, as indicated by the
form of the syntax rules. For example an @code{else} keyword must
be lined up with the corresponding @code{if} keyword.

There are two respects in which the style rule enforced by this check
option are more liberal than those in the Ada Reference Manual. First
in the case of record declarations, it is permissible to put the
@code{record} keyword on the same line as the @code{type} keyword, and
then the @code{end} in @code{end record} must line up under @code{type}.
This is also permitted when the type declaration is split on two lines.
For example, any of the following three layouts is acceptable:

@example
type q is record
   a : integer;
   b : integer;
end record;

type q is
   record
      a : integer;
      b : integer;
   end record;

type q is
   record
      a : integer;
      b : integer;
end record;
@end example

Second, in the case of a block statement, a permitted alternative
is to put the block label on the same line as the @code{declare} or
@code{begin} keyword, and then line the @code{end} keyword up under
the block label. For example both the following are permitted:

@example
Block : declare
   A : Integer := 3;
begin
   Proc (A, A);
end Block;

Block :
   declare
      A : Integer := 3;
   begin
      Proc (A, A);
   end Block;
@end example

The same alternative format is allowed for loops. For example, both of
the following are permitted:

@example
Clear : while J < 10 loop
   A (J) := 0;
end loop Clear;

Clear :
   while J < 10 loop
      A (J) := 0;
   end loop Clear;
@end example
@end table

@geindex -gnatyLnnn (gcc)


@table @asis

@item @code{-gnatyL}

@emph{Set maximum nesting level.}

The maximum level of nesting of constructs (including subprograms, loops,
blocks, packages, and conditionals) may not exceed the given value
@emph{nnn}. A value of zero disconnects this style check.
@end table

@geindex -gnatym (gcc)


@table @asis

@item @code{-gnatym}

@emph{Check maximum line length.}

The length of source lines must not exceed 79 characters, including
any trailing blanks. The value of 79 allows convenient display on an
80 character wide device or window, allowing for possible special
treatment of 80 character lines. Note that this count is of
characters in the source text. This means that a tab character counts
as one character in this count and a wide character sequence counts as
a single character (however many bytes are needed in the encoding).
@end table

@geindex -gnatyMnnn (gcc)


@table @asis

@item @code{-gnatyM}

@emph{Set maximum line length.}

The length of lines must not exceed the
given value @emph{nnn}. The maximum value that can be specified is 32767.
If neither style option for setting the line length is used, then the
default is 255. This also controls the maximum length of lexical elements,
where the only restriction is that they must fit on a single line.
@end table

@geindex -gnatyn (gcc)


@table @asis

@item @code{-gnatyn}

@emph{Check casing of entities in Standard.}

Any identifier from Standard must be cased
to match the presentation in the Ada Reference Manual (for example,
@code{Integer} and @code{ASCII.NUL}).
@end table

@geindex -gnatyN (gcc)


@table @asis

@item @code{-gnatyN}

@emph{Turn off all style checks.}

All style check options are turned off.
@end table

@geindex -gnatyo (gcc)


@table @asis

@item @code{-gnatyo}

@emph{Check order of subprogram bodies.}

All subprogram bodies in a given scope
(e.g., a package body) must be in alphabetical order. The ordering
rule uses normal Ada rules for comparing strings, ignoring casing
of letters, except that if there is a trailing numeric suffix, then
the value of this suffix is used in the ordering (e.g., Junk2 comes
before Junk10).
@end table

@geindex -gnatyO (gcc)


@table @asis

@item @code{-gnatyO}

@emph{Check that overriding subprograms are explicitly marked as such.}

This applies to all subprograms of a derived type that override a primitive
operation of the type, for both tagged and untagged types. In particular,
the declaration of a primitive operation of a type extension that overrides
an inherited operation must carry an overriding indicator. Another case is
the declaration of a function that overrides a predefined operator (such
as an equality operator).
@end table

@geindex -gnatyp (gcc)


@table @asis

@item @code{-gnatyp}

@emph{Check pragma casing.}

Pragma names must be written in mixed case, that is, the
initial letter and any letter following an underscore must be uppercase.
All other letters must be lowercase. An exception is that SPARK_Mode is
allowed as an alternative for Spark_Mode.
@end table

@geindex -gnatyr (gcc)


@table @asis

@item @code{-gnatyr}

@emph{Check references.}

All identifier references must be cased in the same way as the
corresponding declaration. No specific casing style is imposed on
identifiers. The only requirement is for consistency of references
with declarations.
@end table

@geindex -gnatys (gcc)


@table @asis

@item @code{-gnatys}

@emph{Check separate specs.}

Separate declarations ('specs') are required for subprograms (a
body is not allowed to serve as its own declaration). The only
exception is that parameterless library level procedures are
not required to have a separate declaration. This exception covers
the most frequent form of main program procedures.
@end table

@geindex -gnatyS (gcc)


@table @asis

@item @code{-gnatyS}

@emph{Check no statements after then/else.}

No statements are allowed
on the same line as a @code{then} or @code{else} keyword following the
keyword in an @code{if} statement. @code{or else} and @code{and then} are not
affected, and a special exception allows a pragma to appear after @code{else}.
@end table

@geindex -gnatyt (gcc)


@table @asis

@item @code{-gnatyt}

@emph{Check token spacing.}

The following token spacing rules are enforced:


@itemize *

@item 
The keywords @code{abs} and @code{not} must be followed by a space.

@item 
The token @code{=>} must be surrounded by spaces.

@item 
The token @code{<>} must be preceded by a space or a left parenthesis.

@item 
Binary operators other than @code{**} must be surrounded by spaces.
There is no restriction on the layout of the @code{**} binary operator.

@item 
Colon must be surrounded by spaces.

@item 
Colon-equal (assignment, initialization) must be surrounded by spaces.

@item 
Comma must be the first non-blank character on the line, or be
immediately preceded by a non-blank character, and must be followed
by a space.

@item 
If the token preceding a left parenthesis ends with a letter or digit, then
a space must separate the two tokens.

@item 
If the token following a right parenthesis starts with a letter or digit, then
a space must separate the two tokens.

@item 
A right parenthesis must either be the first non-blank character on
a line, or it must be preceded by a non-blank character.

@item 
A semicolon must not be preceded by a space, and must not be followed by
a non-blank character.

@item 
A unary plus or minus may not be followed by a space.

@item 
A vertical bar must be surrounded by spaces.
@end itemize

Exactly one blank (and no other white space) must appear between
a @code{not} token and a following @code{in} token.
@end table

@geindex -gnatyu (gcc)


@table @asis

@item @code{-gnatyu}

@emph{Check unnecessary blank lines.}

Unnecessary blank lines are not allowed. A blank line is considered
unnecessary if it appears at the end of the file, or if more than
one blank line occurs in sequence.
@end table

@geindex -gnatyx (gcc)


@table @asis

@item @code{-gnatyx}

@emph{Check extra parentheses.}