175 lines
7.6 KiB
Plaintext
175 lines
7.6 KiB
Plaintext
@c Copyright (C) 2000, 2001, 2002, 2004 Free Software Foundation, Inc.
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@c This is part of the GCC manual.
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@c For copying conditions, see the file gcc.texi.
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@node Standards
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@chapter Language Standards Supported by GCC
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@cindex C standard
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@cindex C standards
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@cindex ANSI C standard
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@cindex ANSI C
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@cindex ANSI C89
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@cindex C89
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@cindex ANSI X3.159-1989
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@cindex X3.159-1989
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@cindex ISO C standard
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@cindex ISO C
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@cindex ISO C90
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@cindex ISO/IEC 9899
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@cindex ISO 9899
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@cindex C90
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@cindex ISO C94
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@cindex C94
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@cindex ISO C95
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@cindex C95
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@cindex ISO C99
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@cindex C99
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@cindex ISO C9X
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@cindex C9X
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@cindex Technical Corrigenda
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@cindex TC1
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@cindex Technical Corrigendum 1
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@cindex TC2
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@cindex Technical Corrigendum 2
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@cindex AMD1
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@cindex freestanding implementation
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@cindex freestanding environment
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@cindex hosted implementation
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@cindex hosted environment
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@findex __STDC_HOSTED__
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For each language compiled by GCC for which there is a standard, GCC
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attempts to follow one or more versions of that standard, possibly
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with some exceptions, and possibly with some extensions.
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GCC supports three versions of the C standard, although support for
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the most recent version is not yet complete.
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@opindex std
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@opindex ansi
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@opindex pedantic
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@opindex pedantic-errors
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The original ANSI C standard (X3.159-1989) was ratified in 1989 and
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published in 1990. This standard was ratified as an ISO standard
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(ISO/IEC 9899:1990) later in 1990. There were no technical
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differences between these publications, although the sections of the
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ANSI standard were renumbered and became clauses in the ISO standard.
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This standard, in both its forms, is commonly known as @dfn{C89}, or
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occasionally as @dfn{C90}, from the dates of ratification. The ANSI
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standard, but not the ISO standard, also came with a Rationale
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document. To select this standard in GCC, use one of the options
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@option{-ansi}, @option{-std=c89} or @option{-std=iso9899:1990}; to obtain
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all the diagnostics required by the standard, you should also specify
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@option{-pedantic} (or @option{-pedantic-errors} if you want them to be
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errors rather than warnings). @xref{C Dialect Options,,Options
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Controlling C Dialect}.
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Errors in the 1990 ISO C standard were corrected in two Technical
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Corrigenda published in 1994 and 1996. GCC does not support the
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uncorrected version.
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An amendment to the 1990 standard was published in 1995. This
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amendment added digraphs and @code{__STDC_VERSION__} to the language,
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but otherwise concerned the library. This amendment is commonly known
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as @dfn{AMD1}; the amended standard is sometimes known as @dfn{C94} or
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@dfn{C95}. To select this standard in GCC, use the option
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@option{-std=iso9899:199409} (with, as for other standard versions,
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@option{-pedantic} to receive all required diagnostics).
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A new edition of the ISO C standard was published in 1999 as ISO/IEC
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9899:1999, and is commonly known as @dfn{C99}. GCC has incomplete
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support for this standard version; see
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@uref{http://gcc.gnu.org/gcc-4.2/c99status.html} for details. To select this
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standard, use @option{-std=c99} or @option{-std=iso9899:1999}. (While in
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development, drafts of this standard version were referred to as
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@dfn{C9X}.)
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Errors in the 1999 ISO C standard were corrected in two Technical
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Corrigenda published in 2001 and 2004. GCC does not support the uncorrected
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version.
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By default, GCC provides some extensions to the C language that on
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rare occasions conflict with the C standard. @xref{C
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Extensions,,Extensions to the C Language Family}. Use of the
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@option{-std} options listed above will disable these extensions where
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they conflict with the C standard version selected. You may also
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select an extended version of the C language explicitly with
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@option{-std=gnu89} (for C89 with GNU extensions) or @option{-std=gnu99}
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(for C99 with GNU extensions). The default, if no C language dialect
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options are given, is @option{-std=gnu89}; this will change to
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@option{-std=gnu99} in some future release when the C99 support is
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complete. Some features that are part of the C99 standard are
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accepted as extensions in C89 mode.
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The ISO C standard defines (in clause 4) two classes of conforming
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implementation. A @dfn{conforming hosted implementation} supports the
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whole standard including all the library facilities; a @dfn{conforming
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freestanding implementation} is only required to provide certain
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library facilities: those in @code{<float.h>}, @code{<limits.h>},
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@code{<stdarg.h>}, and @code{<stddef.h>}; since AMD1, also those in
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@code{<iso646.h>}; and in C99, also those in @code{<stdbool.h>} and
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@code{<stdint.h>}. In addition, complex types, added in C99, are not
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required for freestanding implementations. The standard also defines
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two environments for programs, a @dfn{freestanding environment},
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required of all implementations and which may not have library
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facilities beyond those required of freestanding implementations,
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where the handling of program startup and termination are
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implementation-defined, and a @dfn{hosted environment}, which is not
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required, in which all the library facilities are provided and startup
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is through a function @code{int main (void)} or @code{int main (int,
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char *[])}. An OS kernel would be a freestanding environment; a
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program using the facilities of an operating system would normally be
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in a hosted implementation.
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@opindex ffreestanding
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GCC aims towards being usable as a conforming freestanding
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implementation, or as the compiler for a conforming hosted
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implementation. By default, it will act as the compiler for a hosted
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implementation, defining @code{__STDC_HOSTED__} as @code{1} and
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presuming that when the names of ISO C functions are used, they have
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the semantics defined in the standard. To make it act as a conforming
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freestanding implementation for a freestanding environment, use the
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option @option{-ffreestanding}; it will then define
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@code{__STDC_HOSTED__} to @code{0} and not make assumptions about the
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meanings of function names from the standard library, with exceptions
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noted below. To build an OS kernel, you may well still need to make
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your own arrangements for linking and startup.
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@xref{C Dialect Options,,Options Controlling C Dialect}.
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GCC does not provide the library facilities required only of hosted
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implementations, nor yet all the facilities required by C99 of
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freestanding implementations; to use the facilities of a hosted
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environment, you will need to find them elsewhere (for example, in the
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GNU C library). @xref{Standard Libraries,,Standard Libraries}.
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Most of the compiler support routines used by GCC are present in
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@file{libgcc}, but there are a few exceptions. GCC requires the
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freestanding environment provide @code{memcpy}, @code{memmove},
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@code{memset} and @code{memcmp}.
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Finally, if @code{__builtin_trap} is used, and the target does
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not implement the @code{trap} pattern, then GCC will emit a call
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to @code{abort}.
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For references to Technical Corrigenda, Rationale documents and
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information concerning the history of C that is available online, see
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@uref{http://gcc.gnu.org/readings.html}
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@c FIXME: details of C++ standard.
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@cindex treelang
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There is no standard for treelang, which is a sample language front end
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for GCC@. Its only purpose is as a sample for people wishing to write a
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new language for GCC@. The language is documented in
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@file{gcc/treelang/treelang.texi} which can be turned into info or
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HTML format.
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@xref{Top, GNAT Reference Manual, About This Guide, gnat_rm,
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GNAT Reference Manual}, for information on standard
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conformance and compatibility of the Ada compiler.
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@xref{Standards,,Standards, gfortran, The GNU Fortran Compiler}, for details
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of standards supported by GNU Fortran.
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@xref{Compatibility,,Compatibility with the Java Platform, gcj, GNU gcj},
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for details of compatibility between @command{gcj} and the Java Platform.
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