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1 @c Copyright (C) 2000, 2001, 2002, 2004, 2006, 2007, 2008 Free Software Foundation,
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2 @c Inc.
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3 @c This is part of the GCC manual.
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4 @c For copying conditions, see the file gcc.texi.
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5
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6 @node Standards
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7 @chapter Language Standards Supported by GCC
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8
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9 For each language compiled by GCC for which there is a standard, GCC
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10 attempts to follow one or more versions of that standard, possibly
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11 with some exceptions, and possibly with some extensions.
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12
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13 @section C language
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14 @cindex C standard
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15 @cindex C standards
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16 @cindex ANSI C standard
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17 @cindex ANSI C
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18 @cindex ANSI C89
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19 @cindex C89
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20 @cindex ANSI X3.159-1989
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21 @cindex X3.159-1989
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22 @cindex ISO C standard
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23 @cindex ISO C
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24 @cindex ISO C90
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25 @cindex ISO/IEC 9899
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26 @cindex ISO 9899
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27 @cindex C90
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28 @cindex ISO C94
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29 @cindex C94
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30 @cindex ISO C95
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31 @cindex C95
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32 @cindex ISO C99
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33 @cindex C99
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34 @cindex ISO C9X
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35 @cindex C9X
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36 @cindex Technical Corrigenda
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37 @cindex TC1
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38 @cindex Technical Corrigendum 1
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39 @cindex TC2
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40 @cindex Technical Corrigendum 2
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41 @cindex TC3
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42 @cindex Technical Corrigendum 3
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43 @cindex AMD1
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44 @cindex freestanding implementation
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45 @cindex freestanding environment
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46 @cindex hosted implementation
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47 @cindex hosted environment
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48 @findex __STDC_HOSTED__
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49
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50 GCC supports three versions of the C standard, although support for
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51 the most recent version is not yet complete.
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52
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53 @opindex std
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54 @opindex ansi
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55 @opindex pedantic
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56 @opindex pedantic-errors
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57 The original ANSI C standard (X3.159-1989) was ratified in 1989 and
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58 published in 1990. This standard was ratified as an ISO standard
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59 (ISO/IEC 9899:1990) later in 1990. There were no technical
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60 differences between these publications, although the sections of the
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61 ANSI standard were renumbered and became clauses in the ISO standard.
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62 This standard, in both its forms, is commonly known as @dfn{C89}, or
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63 occasionally as @dfn{C90}, from the dates of ratification. The ANSI
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64 standard, but not the ISO standard, also came with a Rationale
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65 document. To select this standard in GCC, use one of the options
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66 @option{-ansi}, @option{-std=c89} or @option{-std=iso9899:1990}; to obtain
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67 all the diagnostics required by the standard, you should also specify
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68 @option{-pedantic} (or @option{-pedantic-errors} if you want them to be
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69 errors rather than warnings). @xref{C Dialect Options,,Options
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70 Controlling C Dialect}.
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71
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72 Errors in the 1990 ISO C standard were corrected in two Technical
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73 Corrigenda published in 1994 and 1996. GCC does not support the
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74 uncorrected version.
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75
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76 An amendment to the 1990 standard was published in 1995. This
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77 amendment added digraphs and @code{__STDC_VERSION__} to the language,
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78 but otherwise concerned the library. This amendment is commonly known
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79 as @dfn{AMD1}; the amended standard is sometimes known as @dfn{C94} or
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80 @dfn{C95}. To select this standard in GCC, use the option
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81 @option{-std=iso9899:199409} (with, as for other standard versions,
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82 @option{-pedantic} to receive all required diagnostics).
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83
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84 A new edition of the ISO C standard was published in 1999 as ISO/IEC
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85 9899:1999, and is commonly known as @dfn{C99}. GCC has incomplete
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86 support for this standard version; see
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87 @uref{http://gcc.gnu.org/gcc-4.4/c99status.html} for details. To select this
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88 standard, use @option{-std=c99} or @option{-std=iso9899:1999}. (While in
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89 development, drafts of this standard version were referred to as
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90 @dfn{C9X}.)
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91
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92 Errors in the 1999 ISO C standard were corrected in three Technical
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93 Corrigenda published in 2001, 2004 and 2007. GCC does not support the
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94 uncorrected version.
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95
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96 By default, GCC provides some extensions to the C language that on
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97 rare occasions conflict with the C standard. @xref{C
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98 Extensions,,Extensions to the C Language Family}. Use of the
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99 @option{-std} options listed above will disable these extensions where
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100 they conflict with the C standard version selected. You may also
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101 select an extended version of the C language explicitly with
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102 @option{-std=gnu89} (for C89 with GNU extensions) or @option{-std=gnu99}
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103 (for C99 with GNU extensions). The default, if no C language dialect
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104 options are given, is @option{-std=gnu89}; this will change to
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105 @option{-std=gnu99} in some future release when the C99 support is
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106 complete. Some features that are part of the C99 standard are
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107 accepted as extensions in C89 mode.
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108
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109 The ISO C standard defines (in clause 4) two classes of conforming
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110 implementation. A @dfn{conforming hosted implementation} supports the
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111 whole standard including all the library facilities; a @dfn{conforming
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112 freestanding implementation} is only required to provide certain
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113 library facilities: those in @code{<float.h>}, @code{<limits.h>},
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114 @code{<stdarg.h>}, and @code{<stddef.h>}; since AMD1, also those in
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115 @code{<iso646.h>}; and in C99, also those in @code{<stdbool.h>} and
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116 @code{<stdint.h>}. In addition, complex types, added in C99, are not
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117 required for freestanding implementations. The standard also defines
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118 two environments for programs, a @dfn{freestanding environment},
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119 required of all implementations and which may not have library
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120 facilities beyond those required of freestanding implementations,
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121 where the handling of program startup and termination are
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122 implementation-defined, and a @dfn{hosted environment}, which is not
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123 required, in which all the library facilities are provided and startup
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124 is through a function @code{int main (void)} or @code{int main (int,
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125 char *[])}. An OS kernel would be a freestanding environment; a
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126 program using the facilities of an operating system would normally be
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127 in a hosted implementation.
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128
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129 @opindex ffreestanding
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130 GCC aims towards being usable as a conforming freestanding
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131 implementation, or as the compiler for a conforming hosted
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132 implementation. By default, it will act as the compiler for a hosted
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133 implementation, defining @code{__STDC_HOSTED__} as @code{1} and
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134 presuming that when the names of ISO C functions are used, they have
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135 the semantics defined in the standard. To make it act as a conforming
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136 freestanding implementation for a freestanding environment, use the
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137 option @option{-ffreestanding}; it will then define
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138 @code{__STDC_HOSTED__} to @code{0} and not make assumptions about the
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139 meanings of function names from the standard library, with exceptions
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140 noted below. To build an OS kernel, you may well still need to make
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141 your own arrangements for linking and startup.
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142 @xref{C Dialect Options,,Options Controlling C Dialect}.
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143
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144 GCC does not provide the library facilities required only of hosted
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145 implementations, nor yet all the facilities required by C99 of
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146 freestanding implementations; to use the facilities of a hosted
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147 environment, you will need to find them elsewhere (for example, in the
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148 GNU C library). @xref{Standard Libraries,,Standard Libraries}.
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149
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150 Most of the compiler support routines used by GCC are present in
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151 @file{libgcc}, but there are a few exceptions. GCC requires the
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152 freestanding environment provide @code{memcpy}, @code{memmove},
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153 @code{memset} and @code{memcmp}.
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154 Finally, if @code{__builtin_trap} is used, and the target does
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155 not implement the @code{trap} pattern, then GCC will emit a call
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156 to @code{abort}.
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157
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158 For references to Technical Corrigenda, Rationale documents and
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159 information concerning the history of C that is available online, see
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160 @uref{http://gcc.gnu.org/readings.html}
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161
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162 @section C++ language
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163
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164 GCC supports the ISO C++ standard (1998) and contains experimental
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165 support for the upcoming ISO C++ standard (200x).
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166
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167 The original ISO C++ standard was published as the ISO standard (ISO/IEC
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168 14882:1998) and amended by a Technical Corrigenda published in 2003
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169 (ISO/IEC 14882:2003). These standards are referred to as C++98 and
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170 C++03, respectively. GCC implements the majority of C++98 (@code{export}
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171 is a notable exception) and most of the changes in C++03. To select
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172 this standard in GCC, use one of the options @option{-ansi} or
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173 @option{-std=c++98}; to obtain all the diagnostics required by the
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174 standard, you should also specify @option{-pedantic} (or
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175 @option{-pedantic-errors} if you want them to be errors rather than
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176 warnings).
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177
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178 The ISO C++ committee is working on a new ISO C++ standard, dubbed
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179 C++0x, that is intended to be published by 2009. C++0x contains several
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180 changes to the C++ language, some of which have been implemented in an
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181 experimental C++0x mode in GCC@. The C++0x mode in GCC tracks the draft
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182 working paper for the C++0x standard; the latest working paper is
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183 available on the ISO C++ committee's web site at
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184 @uref{http://www.open-std.org/jtc1/sc22/wg21/}. For information
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185 regarding the C++0x features available in the experimental C++0x mode,
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186 see @uref{http://gcc.gnu.org/gcc-4.3/cxx0x_status.html}. To select this
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187 standard in GCC, use the option @option{-std=c++0x}; to obtain all the
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188 diagnostics required by the standard, you should also specify
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189 @option{-pedantic} (or @option{-pedantic-errors} if you want them to be
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190 errors rather than warnings).
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191
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192 By default, GCC provides some extensions to the C++ language; @xref{C++
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193 Dialect Options,Options Controlling C++ Dialect}. Use of the
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194 @option{-std} option listed above will disable these extensions. You
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195 may also select an extended version of the C++ language explicitly with
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196 @option{-std=gnu++98} (for C++98 with GNU extensions) or
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197 @option{-std=gnu++0x} (for C++0x with GNU extensions). The default, if
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198 no C++ language dialect options are given, is @option{-std=gnu++98}.
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199
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200 @section Objective-C and Objective-C++ languages
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201 @cindex Objective-C
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202 @cindex Objective-C++
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203
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204 There is no formal written standard for Objective-C or Objective-C++@. The most
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205 authoritative manual is ``Object-Oriented Programming and the
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206 Objective-C Language'', available at a number of web sites:
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207
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208 @itemize
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209 @item
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210 @uref{http://developer.apple.com/documentation/Cocoa/Conceptual/ObjectiveC/}
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211 is a recent (and periodically updated) version;
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212 @item
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213 @uref{http://www.toodarkpark.org/computers/objc/}
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214 is an older example;
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215 @item
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216 @uref{http://www.gnustep.org}
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217 and
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218 @uref{http://gcc.gnu.org/readings.html}
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219 have additional useful information.
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220 @end itemize
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221
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222 @xref{Top, GNAT Reference Manual, About This Guide, gnat_rm,
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223 GNAT Reference Manual}, for information on standard
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224 conformance and compatibility of the Ada compiler.
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225
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226 @xref{Standards,,Standards, gfortran, The GNU Fortran Compiler}, for details
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227 of standards supported by GNU Fortran.
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228
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229 @xref{Compatibility,,Compatibility with the Java Platform, gcj, GNU gcj},
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230 for details of compatibility between @command{gcj} and the Java Platform.
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