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 <a name="Standards"></a>
 <div class="header">
 <p>
 Next: <a href="Invoking-GCC.html#Invoking-GCC" accesskey="n" rel="next">Invoking GCC</a>, Previous: <a href="G_002b_002b-and-GCC.html#G_002b_002b-and-GCC" accesskey="p" rel="prev">G++ and GCC</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
 </div>
 <hr>
 <a name="Language-Standards-Supported-by-GCC"></a>
 <h2 class="chapter">2 Language Standards Supported by GCC</h2>

 <p>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.
 </p>
 <a name="C-language"></a>
 <h3 class="section">2.1 C language</h3>
 <a name="index-C-standard"></a>
 <a name="index-C-standards"></a>
 <a name="index-ANSI-C-standard"></a>
 <a name="index-ANSI-C"></a>
 <a name="index-ANSI-C89"></a>
 <a name="index-C89"></a>
 <a name="index-ANSI-X3_002e159_002d1989"></a>
 <a name="index-X3_002e159_002d1989"></a>
 <a name="index-ISO-C-standard"></a>
 <a name="index-ISO-C"></a>
 <a name="index-ISO-C90"></a>
 <a name="index-ISO_002fIEC-9899"></a>
 <a name="index-ISO-9899"></a>
 <a name="index-C90"></a>
 <a name="index-ISO-C94"></a>
 <a name="index-C94"></a>
 <a name="index-ISO-C95"></a>
 <a name="index-C95"></a>
 <a name="index-ISO-C99"></a>
 <a name="index-C99"></a>
 <a name="index-ISO-C9X"></a>
 <a name="index-C9X"></a>
 <a name="index-ISO-C11"></a>
 <a name="index-C11"></a>
 <a name="index-ISO-C1X"></a>
 <a name="index-C1X"></a>
 <a name="index-Technical-Corrigenda"></a>
 <a name="index-TC1"></a>
 <a name="index-Technical-Corrigendum-1"></a>
 <a name="index-TC2"></a>
 <a name="index-Technical-Corrigendum-2"></a>
 <a name="index-TC3"></a>
 <a name="index-Technical-Corrigendum-3"></a>
 <a name="index-AMD1"></a>
 <a name="index-freestanding-implementation"></a>
 <a name="index-freestanding-environment"></a>
 <a name="index-hosted-implementation"></a>
 <a name="index-hosted-environment"></a>
 <a name="index-_005f_005fSTDC_005fHOSTED_005f_005f"></a>

 <p>GCC supports three versions of the C standard, although support for
 the most recent version is not yet complete.
 </p>
 <a name="index-std"></a>
 <a name="index-ansi"></a>
 <a name="index-pedantic"></a>
 <a name="index-pedantic_002derrors"></a>
 <p>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 <em>C89</em>, or
 occasionally as <em>C90</em>, 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
 <samp>-ansi</samp>, <samp>-std=c90</samp> or <samp>-std=iso9899:1990</samp>; to obtain
 all the diagnostics required by the standard, you should also specify
 <samp>-pedantic</samp> (or <samp>-pedantic-errors</samp> if you want them to be
 errors rather than warnings).  See <a href="C-Dialect-Options.html#C-Dialect-Options">Options
 Controlling C Dialect</a>.
 </p>
 <p>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.
 </p>
 <p>An amendment to the 1990 standard was published in 1995.  This
 amendment added digraphs and <code>__STDC_VERSION__</code> to the language,
 but otherwise concerned the library.  This amendment is commonly known
 as <em>AMD1</em>; the amended standard is sometimes known as <em>C94</em> or
 <em>C95</em>.  To select this standard in GCC, use the option
 <samp>-std=iso9899:199409</samp> (with, as for other standard versions,
 <samp>-pedantic</samp> to receive all required diagnostics).
 </p>
 <p>A new edition of the ISO C standard was published in 1999 as ISO/IEC
 9899:1999, and is commonly known as <em>C99</em>.  GCC has substantially
 complete support for this standard version; see
 <a href="http://gcc.gnu.org/c99status.html">http://gcc.gnu.org/c99status.html</a> for details.  To select this
 standard, use <samp>-std=c99</samp> or <samp>-std=iso9899:1999</samp>.  (While in
 development, drafts of this standard version were referred to as
 <em>C9X</em>.)
 </p>
 <p>Errors in the 1999 ISO C standard were corrected in three Technical
 Corrigenda published in 2001, 2004 and 2007.  GCC does not support the
 uncorrected version.
 </p>
 <p>A fourth version of the C standard, known as <em>C11</em>, was published
 in 2011 as ISO/IEC 9899:2011.  GCC has substantially complete support
 for this standard, enabled with <samp>-std=c11</samp> or
 <samp>-std=iso9899:2011</samp>.  (While in development, drafts of this
 standard version were referred to as <em>C1X</em>.)
 </p>
 <p>By default, GCC provides some extensions to the C language that on
 rare occasions conflict with the C standard.  See <a href="C-Extensions.html#C-Extensions">Extensions to the C Language Family</a>.  Use of the
 <samp>-std</samp> 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
 <samp>-std=gnu90</samp> (for C90 with GNU extensions), <samp>-std=gnu99</samp>
 (for C99 with GNU extensions) or <samp>-std=gnu11</samp> (for C11 with GNU
 extensions).  The default, if no C language dialect
 options are given, is <samp>-std=gnu90</samp>; this is intended to change
 to <samp>-std=gnu11</samp> in some future release.  Some features that are
 part of the C99 standard are
 accepted as extensions in C90 mode, and some features that are part of
 the C11 standard are accepted as extensions in C90 and C99 modes.
 </p>
 <p>The ISO C standard defines (in clause 4) two classes of conforming
 implementation.  A <em>conforming hosted implementation</em> supports the
 whole standard including all the library facilities; a <em>conforming
 freestanding implementation</em> is only required to provide certain
 library facilities: those in <code>&lt;float.h&gt;</code>, <code>&lt;limits.h&gt;</code>,
 <code>&lt;stdarg.h&gt;</code>, and <code>&lt;stddef.h&gt;</code>; since AMD1, also those in
 <code>&lt;iso646.h&gt;</code>; since C99, also those in <code>&lt;stdbool.h&gt;</code> and
 <code>&lt;stdint.h&gt;</code>; and since C11, also those in <code>&lt;stdalign.h&gt;</code>
 and <code>&lt;stdnoreturn.h&gt;</code>.  In addition, complex types, added in C99, are not
 required for freestanding implementations.  The standard also defines
 two environments for programs, a <em>freestanding environment</em>,
 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 <em>hosted environment</em>, which is not
 required, in which all the library facilities are provided and startup
 is through a function <code>int main (void)</code> or <code>int main (int,
 char *[])</code>.  An OS kernel would be a freestanding environment; a
 program using the facilities of an operating system would normally be
 in a hosted implementation.
 </p>
 <a name="index-ffreestanding"></a>
 <p>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 <code>__STDC_HOSTED__</code> as <code>1</code> 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 <samp>-ffreestanding</samp>; it will then define
 <code>__STDC_HOSTED__</code> to <code>0</code> 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.
 See <a href="C-Dialect-Options.html#C-Dialect-Options">Options Controlling C Dialect</a>.
 </p>
 <p>GCC does not provide the library facilities required only of hosted
 implementations, nor yet all the facilities required by C99 of
 freestanding implementations on all platforms; to use the facilities of a hosted
 environment, you will need to find them elsewhere (for example, in the
 GNU C library).  See <a href="Standard-Libraries.html#Standard-Libraries">Standard Libraries</a>.
 </p>
 <p>Most of the compiler support routines used by GCC are present in
 <samp>libgcc</samp>, but there are a few exceptions.  GCC requires the
 freestanding environment provide <code>memcpy</code>, <code>memmove</code>,
 <code>memset</code> and <code>memcmp</code>.
 Finally, if <code>__builtin_trap</code> is used, and the target does
 not implement the <code>trap</code> pattern, then GCC will emit a call
 to <code>abort</code>.
 </p>
 <p>For references to Technical Corrigenda, Rationale documents and
 information concerning the history of C that is available online, see
 <a href="http://gcc.gnu.org/readings.html">http://gcc.gnu.org/readings.html</a>
 </p>
 <a name="C_002b_002b-language"></a>
 <h3 class="section">2.2 C++ language</h3>

 <p>GCC supports the original ISO C++ standard (1998) and contains
 experimental support for the second ISO C++ standard (2011).
 </p>
 <p>The original ISO C++ standard was published as the ISO standard (ISO/IEC
 14882:1998) and amended by a Technical Corrigenda published in 2003
 (ISO/IEC 14882:2003). These standards are referred to as C++98 and
 C++03, respectively. GCC implements the majority of C++98 (<code>export</code>
 is a notable exception) and most of the changes in C++03.  To select
 this standard in GCC, use one of the options <samp>-ansi</samp>,
 <samp>-std=c++98</samp>, or <samp>-std=c++03</samp>; to obtain all the diagnostics
 required by the standard, you should also specify <samp>-pedantic</samp> (or
 <samp>-pedantic-errors</samp> if you want them to be errors rather than
 warnings).
 </p>
 <p>A revised ISO C++ standard was published in 2011 as ISO/IEC
 14882:2011, and is referred to as C++11; before its publication it was
 commonly referred to as C++0x.  C++11 contains several
 changes to the C++ language, most of which have been implemented in an
 experimental C++11 mode in GCC.  For information
 regarding the C++11 features available in the experimental C++11 mode,
 see <a href="http://gcc.gnu.org/projects/cxx0x.html">http://gcc.gnu.org/projects/cxx0x.html</a>. To select this
 standard in GCC, use the option <samp>-std=c++11</samp>; to obtain all the
 diagnostics required by the standard, you should also specify
 <samp>-pedantic</samp> (or <samp>-pedantic-errors</samp> if you want them to
 be errors rather than warnings).
 </p>
 <p>More information about the C++ standards is available on the ISO C++
 committee&rsquo;s web site at <a href="http://www.open-std.org/jtc1/sc22/wg21/">http://www.open-std.org/jtc1/sc22/wg21/</a>.
 </p>
 <p>By default, GCC provides some extensions to the C++ language; See <a href="C_002b_002b-Dialect-Options.html#C_002b_002b-Dialect-Options">Options Controlling C++ Dialect</a>.  Use of the
 <samp>-std</samp> option listed above will disable these extensions.  You
 may also select an extended version of the C++ language explicitly with
 <samp>-std=gnu++98</samp> (for C++98 with GNU extensions) or
 <samp>-std=gnu++11</samp> (for C++11 with GNU extensions).  The default, if
 no C++ language dialect options are given, is <samp>-std=gnu++98</samp>.
 </p>
 <a name="Objective_002dC-and-Objective_002dC_002b_002b-languages"></a>
 <h3 class="section">2.3 Objective-C and Objective-C++ languages</h3>
 <a name="index-Objective_002dC-1"></a>
 <a name="index-Objective_002dC_002b_002b-1"></a>

 <p>GCC supports &ldquo;traditional&rdquo; Objective-C (also known as &ldquo;Objective-C
 1.0&rdquo;) and contains support for the Objective-C exception and
 synchronization syntax.  It has also support for a number of
 &ldquo;Objective-C 2.0&rdquo; language extensions, including properties, fast
 enumeration (only for Objective-C), method attributes and the
 @optional and @required keywords in protocols.  GCC supports
 Objective-C++ and features available in Objective-C are also available
 in Objective-C++.
 </p>
 <p>GCC by default uses the GNU Objective-C runtime library, which is part
 of GCC and is not the same as the Apple/NeXT Objective-C runtime
 library used on Apple systems.  There are a number of differences
 documented in this manual.  The options <samp>-fgnu-runtime</samp> and
 <samp>-fnext-runtime</samp> allow you to switch between producing output
 that works with the GNU Objective-C runtime library and output that
 works with the Apple/NeXT Objective-C runtime library.
 </p>
 <p>There is no formal written standard for Objective-C or Objective-C++.
 The authoritative manual on traditional Objective-C (1.0) is
 &ldquo;Object-Oriented Programming and the Objective-C Language&rdquo;,
 available at a number of web sites:
 </p><ul>
 <li> <a href="http://www.gnustep.org/resources/documentation/ObjectivCBook.pdf">http://www.gnustep.org/resources/documentation/ObjectivCBook.pdf</a>
 is the original NeXTstep document;
 </li><li> <a href="http://objc.toodarkpark.net">http://objc.toodarkpark.net</a>
 is the same document in another format;
 </li><li> <a href="http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/ObjectiveC/">http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/ObjectiveC/</a>
 has an updated version but make sure you search for &ldquo;Object Oriented Programming and the Objective-C Programming Language 1.0&rdquo;,
 not documentation on the newer &ldquo;Objective-C 2.0&rdquo; language
 </li></ul>

 <p>The Objective-C exception and synchronization syntax (that is, the
 keywords @try, @throw, @catch, @finally and @synchronized) is
 supported by GCC and is enabled with the option
 <samp>-fobjc-exceptions</samp>.  The syntax is briefly documented in this
 manual and in the Objective-C 2.0 manuals from Apple.
 </p>
 <p>The Objective-C 2.0 language extensions and features are automatically
 enabled; they include properties (via the @property, @synthesize and
 @dynamic keywords), fast enumeration (not available in
 Objective-C++), attributes for methods (such as deprecated, noreturn,
 sentinel, format), the unused attribute for method arguments, the
 @package keyword for instance variables and the @optional and
 @required keywords in protocols.  You can disable all these
 Objective-C 2.0 language extensions with the option
 <samp>-fobjc-std=objc1</samp>, which causes the compiler to recognize the
 same Objective-C language syntax recognized by GCC 4.0, and to produce
 an error if one of the new features is used.
 </p>
 <p>GCC has currently no support for non-fragile instance variables.
 </p>
 <p>The authoritative manual on Objective-C 2.0 is available from Apple:
 </p><ul>
 <li> <a href="http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/ObjectiveC/">http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/ObjectiveC/</a>
 </li></ul>

 <p>For more information concerning the history of Objective-C that is
 available online, see <a href="http://gcc.gnu.org/readings.html">http://gcc.gnu.org/readings.html</a>
 </p>
 <a name="Go-language"></a>
 <h3 class="section">2.4 Go language</h3>

 <p>As of the GCC 4.7.1 release, GCC supports the Go 1 language standard,
 described at <a href="http://golang.org/doc/go1.html">http://golang.org/doc/go1.html</a>.
 </p>
 <a name="References-for-other-languages"></a>
 <h3 class="section">2.5 References for other languages</h3>

 <p>See <a href="http://gcc.gnu.org/onlinedocs/gnat_rm/index.html#Top">About This Guide</a> in <cite>GNAT Reference Manual</cite>, for information on standard
 conformance and compatibility of the Ada compiler.
 </p>
 <p>See <a href="http://gcc.gnu.org/onlinedocs/gfortran/Standards.html#Standards">Standards</a> in <cite>The GNU Fortran Compiler</cite>, for details
 of standards supported by GNU Fortran.
 </p>
 <p>See <a href="http://gcc.gnu.org/onlinedocs/gcj/Compatibility.html#Compatibility">Compatibility with the Java Platform</a> in <cite>GNU gcj</cite>,
 for details of compatibility between <code>gcj</code> and the Java Platform.
 </p>

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	Next: <a href="Invoking-GCC.html#Invoking-GCC" accesskey="n" rel="next">Invoking GCC</a>, Previous: <a href="G_002b_002b-and-GCC.html#G_002b_002b-and-GCC" accesskey="p" rel="prev">G++ and GCC</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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	<hr>
	<a name="Language-Standards-Supported-by-GCC"></a>
	<h2 class="chapter">2 Language Standards Supported by GCC</h2>

	<p>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.
	</p>
	<a name="C-language"></a>
	<h3 class="section">2.1 C language</h3>
	<a name="index-C-standard"></a>
	<a name="index-C-standards"></a>
	<a name="index-ANSI-C-standard"></a>
	<a name="index-ANSI-C"></a>
	<a name="index-ANSI-C89"></a>
	<a name="index-C89"></a>
	<a name="index-ANSI-X3_002e159_002d1989"></a>
	<a name="index-X3_002e159_002d1989"></a>
	<a name="index-ISO-C-standard"></a>
	<a name="index-ISO-C"></a>
	<a name="index-ISO-C90"></a>
	<a name="index-ISO_002fIEC-9899"></a>
	<a name="index-ISO-9899"></a>
	<a name="index-C90"></a>
	<a name="index-ISO-C94"></a>
	<a name="index-C94"></a>
	<a name="index-ISO-C95"></a>
	<a name="index-C95"></a>
	<a name="index-ISO-C99"></a>
	<a name="index-C99"></a>
	<a name="index-ISO-C9X"></a>
	<a name="index-C9X"></a>
	<a name="index-ISO-C11"></a>
	<a name="index-C11"></a>
	<a name="index-ISO-C1X"></a>
	<a name="index-C1X"></a>
	<a name="index-Technical-Corrigenda"></a>
	<a name="index-TC1"></a>
	<a name="index-Technical-Corrigendum-1"></a>
	<a name="index-TC2"></a>
	<a name="index-Technical-Corrigendum-2"></a>
	<a name="index-TC3"></a>
	<a name="index-Technical-Corrigendum-3"></a>
	<a name="index-AMD1"></a>
	<a name="index-freestanding-implementation"></a>
	<a name="index-freestanding-environment"></a>
	<a name="index-hosted-implementation"></a>
	<a name="index-hosted-environment"></a>
	<a name="index-_005f_005fSTDC_005fHOSTED_005f_005f"></a>

	<p>GCC supports three versions of the C standard, although support for
	the most recent version is not yet complete.
	</p>
	<a name="index-std"></a>
	<a name="index-ansi"></a>
	<a name="index-pedantic"></a>
	<a name="index-pedantic_002derrors"></a>
	<p>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 <em>C89</em>, or
	occasionally as <em>C90</em>, 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
	<samp>-ansi</samp>, <samp>-std=c90</samp> or <samp>-std=iso9899:1990</samp>; to obtain
	all the diagnostics required by the standard, you should also specify
	<samp>-pedantic</samp> (or <samp>-pedantic-errors</samp> if you want them to be
	errors rather than warnings). See <a href="C-Dialect-Options.html#C-Dialect-Options">Options
	Controlling C Dialect</a>.
	</p>
	<p>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.
	</p>
	<p>An amendment to the 1990 standard was published in 1995. This
	amendment added digraphs and <code>__STDC_VERSION__</code> to the language,
	but otherwise concerned the library. This amendment is commonly known
	as <em>AMD1</em>; the amended standard is sometimes known as <em>C94</em> or
	<em>C95</em>. To select this standard in GCC, use the option
	<samp>-std=iso9899:199409</samp> (with, as for other standard versions,
	<samp>-pedantic</samp> to receive all required diagnostics).
	</p>
	<p>A new edition of the ISO C standard was published in 1999 as ISO/IEC
	9899:1999, and is commonly known as <em>C99</em>. GCC has substantially
	complete support for this standard version; see
	<a href="http://gcc.gnu.org/c99status.html">http://gcc.gnu.org/c99status.html</a> for details. To select this
	standard, use <samp>-std=c99</samp> or <samp>-std=iso9899:1999</samp>. (While in
	development, drafts of this standard version were referred to as
	<em>C9X</em>.)
	</p>
	<p>Errors in the 1999 ISO C standard were corrected in three Technical
	Corrigenda published in 2001, 2004 and 2007. GCC does not support the
	uncorrected version.
	</p>
	<p>A fourth version of the C standard, known as <em>C11</em>, was published
	in 2011 as ISO/IEC 9899:2011. GCC has substantially complete support
	for this standard, enabled with <samp>-std=c11</samp> or
	<samp>-std=iso9899:2011</samp>. (While in development, drafts of this
	standard version were referred to as <em>C1X</em>.)
	</p>
	<p>By default, GCC provides some extensions to the C language that on
	rare occasions conflict with the C standard. See <a href="C-Extensions.html#C-Extensions">Extensions to the C Language Family</a>. Use of the
	<samp>-std</samp> 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
	<samp>-std=gnu90</samp> (for C90 with GNU extensions), <samp>-std=gnu99</samp>
	(for C99 with GNU extensions) or <samp>-std=gnu11</samp> (for C11 with GNU
	extensions). The default, if no C language dialect
	options are given, is <samp>-std=gnu90</samp>; this is intended to change
	to <samp>-std=gnu11</samp> in some future release. Some features that are
	part of the C99 standard are
	accepted as extensions in C90 mode, and some features that are part of
	the C11 standard are accepted as extensions in C90 and C99 modes.
	</p>
	<p>The ISO C standard defines (in clause 4) two classes of conforming
	implementation. A <em>conforming hosted implementation</em> supports the
	whole standard including all the library facilities; a <em>conforming
	freestanding implementation</em> is only required to provide certain
	library facilities: those in <code><float.h></code>, <code><limits.h></code>,
	<code><stdarg.h></code>, and <code><stddef.h></code>; since AMD1, also those in
	<code><iso646.h></code>; since C99, also those in <code><stdbool.h></code> and
	<code><stdint.h></code>; and since C11, also those in <code><stdalign.h></code>
	and <code><stdnoreturn.h></code>. In addition, complex types, added in C99, are not
	required for freestanding implementations. The standard also defines
	two environments for programs, a <em>freestanding environment</em>,
	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 <em>hosted environment</em>, which is not
	required, in which all the library facilities are provided and startup
	is through a function <code>int main (void)</code> or <code>int main (int,
	char *[])</code>. An OS kernel would be a freestanding environment; a
	program using the facilities of an operating system would normally be
	in a hosted implementation.
	</p>
	<a name="index-ffreestanding"></a>
	<p>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 <code>__STDC_HOSTED__</code> as <code>1</code> 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 <samp>-ffreestanding</samp>; it will then define
	<code>__STDC_HOSTED__</code> to <code>0</code> 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.
	See <a href="C-Dialect-Options.html#C-Dialect-Options">Options Controlling C Dialect</a>.
	</p>
	<p>GCC does not provide the library facilities required only of hosted
	implementations, nor yet all the facilities required by C99 of
	freestanding implementations on all platforms; to use the facilities of a hosted
	environment, you will need to find them elsewhere (for example, in the
	GNU C library). See <a href="Standard-Libraries.html#Standard-Libraries">Standard Libraries</a>.
	</p>
	<p>Most of the compiler support routines used by GCC are present in
	<samp>libgcc</samp>, but there are a few exceptions. GCC requires the
	freestanding environment provide <code>memcpy</code>, <code>memmove</code>,
	<code>memset</code> and <code>memcmp</code>.
	Finally, if <code>__builtin_trap</code> is used, and the target does
	not implement the <code>trap</code> pattern, then GCC will emit a call
	to <code>abort</code>.
	</p>
	<p>For references to Technical Corrigenda, Rationale documents and
	information concerning the history of C that is available online, see
	<a href="http://gcc.gnu.org/readings.html">http://gcc.gnu.org/readings.html</a>
	</p>
	<a name="C_002b_002b-language"></a>
	<h3 class="section">2.2 C++ language</h3>

	<p>GCC supports the original ISO C++ standard (1998) and contains
	experimental support for the second ISO C++ standard (2011).
	</p>
	<p>The original ISO C++ standard was published as the ISO standard (ISO/IEC
	14882:1998) and amended by a Technical Corrigenda published in 2003
	(ISO/IEC 14882:2003). These standards are referred to as C++98 and
	C++03, respectively. GCC implements the majority of C++98 (<code>export</code>
	is a notable exception) and most of the changes in C++03. To select
	this standard in GCC, use one of the options <samp>-ansi</samp>,
	<samp>-std=c++98</samp>, or <samp>-std=c++03</samp>; to obtain all the diagnostics
	required by the standard, you should also specify <samp>-pedantic</samp> (or
	<samp>-pedantic-errors</samp> if you want them to be errors rather than
	warnings).
	</p>
	<p>A revised ISO C++ standard was published in 2011 as ISO/IEC
	14882:2011, and is referred to as C++11; before its publication it was
	commonly referred to as C++0x. C++11 contains several
	changes to the C++ language, most of which have been implemented in an
	experimental C++11 mode in GCC. For information
	regarding the C++11 features available in the experimental C++11 mode,
	see <a href="http://gcc.gnu.org/projects/cxx0x.html">http://gcc.gnu.org/projects/cxx0x.html</a>. To select this
	standard in GCC, use the option <samp>-std=c++11</samp>; to obtain all the
	diagnostics required by the standard, you should also specify
	<samp>-pedantic</samp> (or <samp>-pedantic-errors</samp> if you want them to
	be errors rather than warnings).
	</p>
	<p>More information about the C++ standards is available on the ISO C++
	committee’s web site at <a href="http://www.open-std.org/jtc1/sc22/wg21/">http://www.open-std.org/jtc1/sc22/wg21/</a>.
	</p>
	<p>By default, GCC provides some extensions to the C++ language; See <a href="C_002b_002b-Dialect-Options.html#C_002b_002b-Dialect-Options">Options Controlling C++ Dialect</a>. Use of the
	<samp>-std</samp> option listed above will disable these extensions. You
	may also select an extended version of the C++ language explicitly with
	<samp>-std=gnu++98</samp> (for C++98 with GNU extensions) or
	<samp>-std=gnu++11</samp> (for C++11 with GNU extensions). The default, if
	no C++ language dialect options are given, is <samp>-std=gnu++98</samp>.
	</p>
	<a name="Objective_002dC-and-Objective_002dC_002b_002b-languages"></a>
	<h3 class="section">2.3 Objective-C and Objective-C++ languages</h3>
	<a name="index-Objective_002dC-1"></a>
	<a name="index-Objective_002dC_002b_002b-1"></a>

	<p>GCC supports “traditional” Objective-C (also known as “Objective-C
	1.0”) and contains support for the Objective-C exception and
	synchronization syntax. It has also support for a number of
	“Objective-C 2.0” language extensions, including properties, fast
	enumeration (only for Objective-C), method attributes and the
	@optional and @required keywords in protocols. GCC supports
	Objective-C++ and features available in Objective-C are also available
	in Objective-C++.
	</p>
	<p>GCC by default uses the GNU Objective-C runtime library, which is part
	of GCC and is not the same as the Apple/NeXT Objective-C runtime
	library used on Apple systems. There are a number of differences
	documented in this manual. The options <samp>-fgnu-runtime</samp> and
	<samp>-fnext-runtime</samp> allow you to switch between producing output
	that works with the GNU Objective-C runtime library and output that
	works with the Apple/NeXT Objective-C runtime library.
	</p>
	<p>There is no formal written standard for Objective-C or Objective-C++.
	The authoritative manual on traditional Objective-C (1.0) is
	“Object-Oriented Programming and the Objective-C Language”,
	available at a number of web sites:
	</p><ul>
	<li> <a href="http://www.gnustep.org/resources/documentation/ObjectivCBook.pdf">http://www.gnustep.org/resources/documentation/ObjectivCBook.pdf</a>
	is the original NeXTstep document;
	</li><li> <a href="http://objc.toodarkpark.net">http://objc.toodarkpark.net</a>
	is the same document in another format;
	</li><li> <a href="http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/ObjectiveC/">http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/ObjectiveC/</a>
	has an updated version but make sure you search for “Object Oriented Programming and the Objective-C Programming Language 1.0”,
	not documentation on the newer “Objective-C 2.0” language
	</li></ul>

	<p>The Objective-C exception and synchronization syntax (that is, the
	keywords @try, @throw, @catch, @finally and @synchronized) is
	supported by GCC and is enabled with the option
	<samp>-fobjc-exceptions</samp>. The syntax is briefly documented in this
	manual and in the Objective-C 2.0 manuals from Apple.
	</p>
	<p>The Objective-C 2.0 language extensions and features are automatically
	enabled; they include properties (via the @property, @synthesize and
	@dynamic keywords), fast enumeration (not available in
	Objective-C++), attributes for methods (such as deprecated, noreturn,
	sentinel, format), the unused attribute for method arguments, the
	@package keyword for instance variables and the @optional and
	@required keywords in protocols. You can disable all these
	Objective-C 2.0 language extensions with the option
	<samp>-fobjc-std=objc1</samp>, which causes the compiler to recognize the
	same Objective-C language syntax recognized by GCC 4.0, and to produce
	an error if one of the new features is used.
	</p>
	<p>GCC has currently no support for non-fragile instance variables.
	</p>
	<p>The authoritative manual on Objective-C 2.0 is available from Apple:
	</p><ul>
	<li> <a href="http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/ObjectiveC/">http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/ObjectiveC/</a>
	</li></ul>

	<p>For more information concerning the history of Objective-C that is
	available online, see <a href="http://gcc.gnu.org/readings.html">http://gcc.gnu.org/readings.html</a>
	</p>
	<a name="Go-language"></a>
	<h3 class="section">2.4 Go language</h3>

	<p>As of the GCC 4.7.1 release, GCC supports the Go 1 language standard,
	described at <a href="http://golang.org/doc/go1.html">http://golang.org/doc/go1.html</a>.
	</p>
	<a name="References-for-other-languages"></a>
	<h3 class="section">2.5 References for other languages</h3>

	<p>See <a href="http://gcc.gnu.org/onlinedocs/gnat_rm/index.html#Top">About This Guide</a> in <cite>GNAT Reference Manual</cite>, for information on standard
	conformance and compatibility of the Ada compiler.
	</p>
	<p>See <a href="http://gcc.gnu.org/onlinedocs/gfortran/Standards.html#Standards">Standards</a> in <cite>The GNU Fortran Compiler</cite>, for details
	of standards supported by GNU Fortran.
	</p>
	<p>See <a href="http://gcc.gnu.org/onlinedocs/gcj/Compatibility.html#Compatibility">Compatibility with the Java Platform</a> in <cite>GNU gcj</cite>,
	for details of compatibility between <code>gcj</code> and the Java Platform.
	</p>

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