gcc/doc/standards.texi

   1 @c Copyright (C) 2000, 2001 Free Software Foundation, Inc.
   2 @c This is part of the GCC manual.
   3 @c For copying conditions, see the file gcc.texi.
   4
   5 @node Standards
   6 @chapter Language Standards Supported by GCC
   7 @cindex C standard
   8 @cindex C standards
   9 @cindex ANSI C standard
  10 @cindex ANSI C
  11 @cindex ANSI C89
  12 @cindex C89
  13 @cindex ANSI X3.159-1989
  14 @cindex X3.159-1989
  15 @cindex ISO C standard
  16 @cindex ISO C
  17 @cindex ISO C89
  18 @cindex ISO C90
  19 @cindex ISO/IEC 9899
  20 @cindex ISO 9899
  21 @cindex C90
  22 @cindex ISO C94
  23 @cindex C94
  24 @cindex ISO C95
  25 @cindex C95
  26 @cindex ISO C99
  27 @cindex C99
  28 @cindex ISO C9X
  29 @cindex C9X
  30 @cindex Technical Corrigenda
  31 @cindex TC1
  32 @cindex Technical Corrigendum 1
  33 @cindex TC2
  34 @cindex Technical Corrigendum 2
  35 @cindex AMD1
  36 @cindex freestanding implementation
  37 @cindex freestanding environment
  38 @cindex hosted implementation
  39 @cindex hosted environment
  40 @findex __STDC_HOSTED__
  41
  42 For each language compiled by GCC for which there is a standard, GCC
  43 attempts to follow one or more versions of that standard, possibly
  44 with some exceptions, and possibly with some extensions.
  45
  46 GCC supports three versions of the C standard, although support for
  47 the most recent version is not yet complete.
  48
  49 @opindex std
  50 @opindex ansi
  51 @opindex pedantic
  52 @opindex pedantic-errors
  53 The original ANSI C standard (X3.159-1989) was ratified in 1989 and
  54 published in 1990.  This standard was ratified as an ISO standard
  55 (ISO/IEC 9899:1990) later in 1990.  There were no technical
  56 differences between these publications, although the sections of the
  57 ANSI standard were renumbered and became clauses in the ISO standard.
  58 This standard, in both its forms, is commonly known as @dfn{C89}, or
  59 occasionally as @dfn{C90}, from the dates of ratification.  The ANSI
  60 standard, but not the ISO standard, also came with a Rationale
  61 document.  To select this standard in GCC, use one of the options
  62 @option{-ansi}, @option{-std=c89} or @option{-std=iso9899:1990}; to obtain
  63 all the diagnostics required by the standard, you should also specify
  64 @option{-pedantic} (or @option{-pedantic-errors} if you want them to be
  65 errors rather than warnings).  @xref{C Dialect Options,,Options
  66 Controlling C Dialect}.
  67
  68 Errors in the 1990 ISO C standard were corrected in two Technical
  69 Corrigenda published in 1994 and 1996.  GCC does not support the
  70 uncorrected version.
  71
  72 An amendment to the 1990 standard was published in 1995.  This
  73 amendment added digraphs and @code{__STDC_VERSION__} to the language,
  74 but otherwise concerned the library.  This amendment is commonly known
  75 as @dfn{AMD1}; the amended standard is sometimes known as @dfn{C94} or
  76 @dfn{C95}.  To select this standard in GCC, use the option
  77 @option{-std=iso9899:199409} (with, as for other standard versions,
  78 @option{-pedantic} to receive all required diagnostics).
  79
  80 A new edition of the ISO C standard was published in 1999 as ISO/IEC
  81 9899:1999, and is commonly known as @dfn{C99}.  GCC has incomplete
  82 support for this standard version; see
  83 @uref{http://gcc.gnu.org/c99status.html} for details.  To select this
  84 standard, use @option{-std=c99} or @option{-std=iso9899:1999}.  (While in
  85 development, drafts of this standard version were referred to as
  86 @dfn{C9X}.)
  87
  88 Errors in the 1999 ISO C standard were corrected in a Technical
  89 Corrigendum published in 2001.  GCC does not support the uncorrected
  90 version.
  91
  92 @opindex traditional
  93 GCC also has some limited support for traditional (pre-ISO) C with the
  94 @option{-traditional} option.  This support may be of use for compiling
  95 some very old programs that have not been updated to ISO C, but should
  96 not be used for new programs.  It will not work with some modern C
  97 libraries such as the GNU C library.
  98
  99 By default, GCC provides some extensions to the C language that on
 100 rare occasions conflict with the C standard.  @xref{C
 101 Extensions,,Extensions to the C Language Family}.  Use of the
 102 @option{-std} options listed above will disable these extensions where
 103 they conflict with the C standard version selected.  You may also
 104 select an extended version of the C language explicitly with
 105 @option{-std=gnu89} (for C89 with GNU extensions) or @option{-std=gnu99}
 106 (for C99 with GNU extensions).  The default, if no C language dialect
 107 options are given, is @option{-std=gnu89}; this will change to
 108 @option{-std=gnu99} in some future release when the C99 support is
 109 complete.  Some features that are part of the C99 standard are
 110 accepted as extensions in C89 mode.
 111
 112 The ISO C standard defines (in clause 4) two classes of conforming
 113 implementation.  A @dfn{conforming hosted implementation} supports the
 114 whole standard including all the library facilities; a @dfn{conforming
 115 freestanding implementation} is only required to provide certain
 116 library facilities: those in @code{<float.h>}, @code{<limits.h>},
 117 @code{<stdarg.h>}, and @code{<stddef.h>}; since AMD1, also those in
 118 @code{<iso646.h>}; and in C99, also those in @code{<stdbool.h>} and
 119 @code{<stdint.h>}.  In addition, complex types, added in C99, are not
 120 required for freestanding implementations.  The standard also defines
 121 two environments for programs, a @dfn{freestanding environment},
 122 required of all implementations and which may not have library
 123 facilities beyond those required of freestanding implementations,
 124 where the handling of program startup and termination are
 125 implementation-defined, and a @dfn{hosted environment}, which is not
 126 required, in which all the library facilities are provided and startup
 127 is through a function @code{int main (void)} or @code{int main (int,
 128 char *[])}.  An OS kernel would be a freestanding environment; a
 129 program using the facilities of an operating system would normally be
 130 in a hosted implementation.
 131
 132 @opindex ffreestanding
 133 GCC aims towards being usable as a conforming freestanding
 134 implementation, or as the compiler for a conforming hosted
 135 implementation.  By default, it will act as the compiler for a hosted
 136 implementation, defining @code{__STDC_HOSTED__} as @code{1} and
 137 presuming that when the names of ISO C functions are used, they have
 138 the semantics defined in the standard.  To make it act as a conforming
 139 freestanding implementation for a freestanding environment, use the
 140 option @option{-ffreestanding}; it will then define
 141 @code{__STDC_HOSTED__} to @code{0} and not make assumptions about the
 142 meanings of function names from the standard library.  To build an OS
 143 kernel, you may well still need to make your own arrangements for
 144 linking and startup.  @xref{C Dialect Options,,Options Controlling C
 145 Dialect}.
 146
 147 GCC does not provide the library facilities required only of hosted
 148 implementations, nor yet all the facilities required by C99 of
 149 freestanding implementations; to use the facilities of a hosted
 150 environment, you will need to find them elsewhere (for example, in the
 151 GNU C library).  @xref{Standard Libraries,,Standard Libraries}.
 152
 153 For references to Technical Corrigenda, Rationale documents and
 154 information concerning the history of C that is available online, see
 155 @uref{http://gcc.gnu.org/readings.html}
 156
 157 @c FIXME: details of C++ standard.
 158
 159 There is no formal written standard for Objective-C@.  The most
 160 authoritative manual is ``Object-Oriented Programming and the
 161 Objective-C Language'', available at a number of web sites;
 162 @uref{http://developer.apple.com/techpubs/macosx/Cocoa/ObjectiveC/} has a
 163 recent version, while @uref{http://www.toodarkpark.org/computers/objc/}
 164 is an older example.  @uref{http://www.gnustep.org} includes useful
 165 information as well.
 166
 167 @xref{Top, GNAT Reference Manual, About This Guide, gnat_rm,
 168 GNAT Reference Manual}, for information on standard
 169 conformance and compatibility of the Ada compiler.
 170
 171 @xref{References,,Language Definition References, chill, GNU Chill},
 172 for details of the CHILL standard.
 173
 174 @xref{Language,,The GNU Fortran Language, g77, Using and Porting GNU
 175 Fortran}, for details of the Fortran language supported by GCC@.
 176
 177 @xref{Compatibility,,Compatibility with the Java Platform, gcj, GNU gcj},
 178 for details of compatibility between @code{gcj} and the Java Platform.