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Language Standards Supported by GCC

   For each language compiled by GCC for which there is a standard, GCC
attempts to follow one or more versions of that standard, possibly with
some exceptions, and possibly with some extensions.
   GCC supports three versions of the C standard, although support for
the most recent version is not yet complete.
   The original ANSI C standard (X3.159-1989) was ratified in 1989 and
published in 1990.  This standard was ratified as an ISO standard
(ISO/IEC 9899:1990) later in 1990.  There were no technical differences
between these publications, although the sections of the ANSI standard
were renumbered and became clauses in the ISO standard.  This standard,
in both its forms, is commonly known as "C89", or occasionally as
"C90", from the dates of ratification.  The ANSI standard, but not the
ISO standard, also came with a Rationale document.  To select this
standard in GCC, use one of the options `-ansi', `-std=c89' or
`-std=iso9899:1990'; to obtain all the diagnostics required by the
standard, you should also specify `-pedantic' (or `-pedantic-errors' if
you want them to be errors rather than warnings).  *Note Options
Controlling C Dialect: C Dialect Options.
   Errors in the 1990 ISO C standard were corrected in two Technical
Corrigenda published in 1994 and 1996.  GCC does not support the
uncorrected version.
   An amendment to the 1990 standard was published in 1995.  This
amendment added digraphs and `__STDC_VERSION__' to the language, but
otherwise concerned the library.  This amendment is commonly known as
"AMD1"; the amended standard is sometimes known as "C94" or "C95".  To
select this standard in GCC, use the option `-std=iso9899:199409'
(with, as for other standard versions, `-pedantic' to receive all
required diagnostics).
   A new edition of the ISO C standard was published in 1999 as ISO/IEC
9899:1999, and is commonly known as "C99".  GCC has incomplete support
for this standard version; see
`http://gcc.gnu.org/gcc-3.1/c99status.html' for details.  To select this
standard, use `-std=c99' or `-std=iso9899:1999'.  (While in
development, drafts of this standard version were referred to as "C9X".)
   Errors in the 1999 ISO C standard were corrected in a Technical
Corrigendum published in 2001.  GCC does not support the uncorrected
version.
   GCC also has some limited support for traditional (pre-ISO) C with
the `-traditional' option.  This support may be of use for compiling
some very old programs that have not been updated to ISO C, but should
not be used for new programs.  It will not work with some modern C
libraries such as the GNU C library.
   By default, GCC provides some extensions to the C language that on
rare occasions conflict with the C standard.  *Note Extensions to the C
Language Family: C Extensions.  Use of the `-std' options listed above
will disable these extensions where they conflict with the C standard
version selected.  You may also select an extended version of the C
language explicitly with `-std=gnu89' (for C89 with GNU extensions) or
`-std=gnu99' (for C99 with GNU extensions).  The default, if no C
language dialect options are given, is `-std=gnu89'; this will change to
`-std=gnu99' in some future release when the C99 support is complete.
Some features that are part of the C99 standard are accepted as
extensions in C89 mode.
   The ISO C standard defines (in clause 4) two classes of conforming
implementation.  A "conforming hosted implementation" supports the
whole standard including all the library facilities; a "conforming
freestanding implementation" is only required to provide certain
library facilities: those in `<float.h>', `<limits.h>', `<stdarg.h>',
and `<stddef.h>'; since AMD1, also those in `<iso646.h>'; and in C99,
also those in `<stdbool.h>' and `<stdint.h>'.  In addition, complex
types, added in C99, are not required for freestanding implementations.
The standard also defines two environments for programs, a
"freestanding environment", required of all implementations and which
may not have library facilities beyond those required of freestanding
implementations, where the handling of program startup and termination
are implementation-defined, and a "hosted environment", which is not
required, in which all the library facilities are provided and startup
is through a function `int main (void)' or `int main (int, char *[])'.
An OS kernel would be a freestanding environment; a program using the
facilities of an operating system would normally be in a hosted
implementation.
   GCC aims towards being usable as a conforming freestanding
implementation, or as the compiler for a conforming hosted
implementation.  By default, it will act as the compiler for a hosted
implementation, defining `__STDC_HOSTED__' as `1' and presuming that
when the names of ISO C functions are used, they have the semantics
defined in the standard.  To make it act as a conforming freestanding
implementation for a freestanding environment, use the option
`-ffreestanding'; it will then define `__STDC_HOSTED__' to `0' and not
make assumptions about the meanings of function names from the standard
library, with exceptions noted below.  To build an OS kernel, you may
well still need to make your own arrangements for linking and startup.
*Note Options Controlling C Dialect: C Dialect Options.
   GCC does not provide the library facilities required only of hosted
implementations, nor yet all the facilities required by C99 of
freestanding implementations; to use the facilities of a hosted
environment, you will need to find them elsewhere (for example, in the
GNU C library).  *Note Standard Libraries: Standard Libraries.
   Most of the compiler support routines used by GCC are present in
`libgcc', but there are a few exceptions.  GCC requires the
freestanding environment provide `memcpy', `memmove', `memset' and
`memcmp'.  Some older ports of GCC are configured to use the BSD
`bcopy', `bzero' and `bcmp' functions instead, but this is deprecated
for new ports.  Finally, if `__builtin_trap' is used, and the target
does not implement the `trap' pattern, then GCC will emit a call to
`abort'.
   For references to Technical Corrigenda, Rationale documents and
information concerning the history of C that is available online, see
`http://gcc.gnu.org/readings.html'
   There is no formal written standard for Objective-C.  The most
authoritative manual is "Object-Oriented Programming and the
Objective-C Language", available at a number of web sites
   * `http://developer.apple.com/techpubs/macosx/Cocoa/ObjectiveC/' is
     a recent version
   * `http://www.toodarkpark.org/computers/objc/' is an older example
   * `http://www.gnustep.org' has additional useful information
   *Note GNAT Reference Manual: (gnat_rm)Top, for information on
standard conformance and compatibility of the Ada compiler.
   *Note The GNU Fortran Language: (g77)Language, for details of the
Fortran language supported by GCC.
   *Note Compatibility with the Java Platform: (gcj)Compatibility, for
details of compatibility between `gcj' and the Java Platform.