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1 @c Copyright (C) 1999-2020 Free Software Foundation, Inc.
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2 @c This is part of the CPP and GCC manuals.
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3 @c For copying conditions, see the file gcc.texi.
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4
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5 @c ---------------------------------------------------------------------
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6 @c Environment variables affecting the preprocessor
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7 @c ---------------------------------------------------------------------
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8
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9 @c If this file is included with the flag ``cppmanual'' set, it is
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10 @c formatted for inclusion in the CPP manual; otherwise the main GCC manual.
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11
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12 @vtable @env
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13 @item CPATH
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14 @itemx C_INCLUDE_PATH
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15 @itemx CPLUS_INCLUDE_PATH
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16 @itemx OBJC_INCLUDE_PATH
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17 @c Commented out until ObjC++ is part of GCC:
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18 @c @itemx OBJCPLUS_INCLUDE_PATH
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19 Each variable's value is a list of directories separated by a special
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20 character, much like @env{PATH}, in which to look for header files.
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21 The special character, @code{PATH_SEPARATOR}, is target-dependent and
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22 determined at GCC build time. For Microsoft Windows-based targets it is a
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23 semicolon, and for almost all other targets it is a colon.
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24
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25 @env{CPATH} specifies a list of directories to be searched as if
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26 specified with @option{-I}, but after any paths given with @option{-I}
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27 options on the command line. This environment variable is used
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28 regardless of which language is being preprocessed.
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29
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30 The remaining environment variables apply only when preprocessing the
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31 particular language indicated. Each specifies a list of directories
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32 to be searched as if specified with @option{-isystem}, but after any
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33 paths given with @option{-isystem} options on the command line.
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34
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35 In all these variables, an empty element instructs the compiler to
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36 search its current working directory. Empty elements can appear at the
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37 beginning or end of a path. For instance, if the value of
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38 @env{CPATH} is @code{:/special/include}, that has the same
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39 effect as @samp{@w{-I. -I/special/include}}.
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40
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41 @c man end
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42 @ifset cppmanual
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43 See also @ref{Search Path}.
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44 @end ifset
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45 @c man begin ENVIRONMENT
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46
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47 @item DEPENDENCIES_OUTPUT
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48 @cindex dependencies for make as output
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49 If this variable is set, its value specifies how to output
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50 dependencies for Make based on the non-system header files processed
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51 by the compiler. System header files are ignored in the dependency
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52 output.
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53
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54 The value of @env{DEPENDENCIES_OUTPUT} can be just a file name, in
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55 which case the Make rules are written to that file, guessing the target
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56 name from the source file name. Or the value can have the form
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57 @samp{@var{file} @var{target}}, in which case the rules are written to
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58 file @var{file} using @var{target} as the target name.
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59
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60 In other words, this environment variable is equivalent to combining
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61 the options @option{-MM} and @option{-MF}
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62 @ifset cppmanual
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63 (@pxref{Invocation}),
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64 @end ifset
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65 @ifclear cppmanual
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66 (@pxref{Preprocessor Options}),
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67 @end ifclear
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68 with an optional @option{-MT} switch too.
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69
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70 @item SUNPRO_DEPENDENCIES
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71 @cindex dependencies for make as output
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72 This variable is the same as @env{DEPENDENCIES_OUTPUT} (see above),
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73 except that system header files are not ignored, so it implies
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74 @option{-M} rather than @option{-MM}. However, the dependence on the
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75 main input file is omitted.
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76 @ifset cppmanual
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77 @xref{Invocation}.
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78 @end ifset
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79 @ifclear cppmanual
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80 @xref{Preprocessor Options}.
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81 @end ifclear
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111
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82
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83 @item SOURCE_DATE_EPOCH
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84 If this variable is set, its value specifies a UNIX timestamp to be
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85 used in replacement of the current date and time in the @code{__DATE__}
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86 and @code{__TIME__} macros, so that the embedded timestamps become
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87 reproducible.
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88
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89 The value of @env{SOURCE_DATE_EPOCH} must be a UNIX timestamp,
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90 defined as the number of seconds (excluding leap seconds) since
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91 01 Jan 1970 00:00:00 represented in ASCII; identical to the output of
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92 @samp{@command{date +%s}} on GNU/Linux and other systems that support the
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93 @code{%s} extension in the @code{date} command.
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94
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95 The value should be a known timestamp such as the last modification
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96 time of the source or package and it should be set by the build
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97 process.
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98
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99 @end vtable
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