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<a name="C-Implementation"></a>
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<p>
Next: <a href="C_002b_002b-Implementation.html#C_002b_002b-Implementation" accesskey="n" rel="next">C++ Implementation</a>, Previous: <a href="Invoking-GCC.html#Invoking-GCC" accesskey="p" rel="prev">Invoking 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>
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<a name="C-Implementation_002dDefined-Behavior"></a>
<h2 class="chapter">4 C Implementation-Defined Behavior</h2>
<a name="index-implementation_002ddefined-behavior_002c-C-language"></a>

<p>A conforming implementation of ISO C is required to document its
choice of behavior in each of the areas that are designated
&ldquo;implementation defined&rdquo;.  The following lists all such areas,
along with the section numbers from the ISO/IEC 9899:1990, ISO/IEC
9899:1999 and ISO/IEC 9899:2011 standards.  Some areas are only
implementation-defined in one version of the standard.
</p>
<p>Some choices depend on the externally determined ABI for the platform
(including standard character encodings) which GCC follows; these are
listed as &ldquo;determined by ABI&rdquo; below.  See <a href="Compatibility.html#Compatibility">Binary
Compatibility</a>, and <a href="http://gcc.gnu.org/readings.html">http://gcc.gnu.org/readings.html</a>.  Some
choices are documented in the preprocessor manual.
See <a href="http://gcc.gnu.org/onlinedocs/cpp/Implementation_002ddefined-behavior.html#Implementation_002ddefined-behavior">Implementation-defined
behavior</a> in <cite>The C Preprocessor</cite>.  Some choices are made by the
library and operating system (or other environment when compiling for
a freestanding environment); refer to their documentation for details.
</p>
<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top">&bull; <a href="Translation-implementation.html#Translation-implementation" accesskey="1">Translation implementation</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Environment-implementation.html#Environment-implementation" accesskey="2">Environment implementation</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Identifiers-implementation.html#Identifiers-implementation" accesskey="3">Identifiers implementation</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Characters-implementation.html#Characters-implementation" accesskey="4">Characters implementation</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Integers-implementation.html#Integers-implementation" accesskey="5">Integers implementation</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Floating-point-implementation.html#Floating-point-implementation" accesskey="6">Floating point implementation</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Arrays-and-pointers-implementation.html#Arrays-and-pointers-implementation" accesskey="7">Arrays and pointers implementation</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Hints-implementation.html#Hints-implementation" accesskey="8">Hints implementation</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Structures-unions-enumerations-and-bit_002dfields-implementation.html#Structures-unions-enumerations-and-bit_002dfields-implementation" accesskey="9">Structures unions enumerations and bit-fields implementation</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Qualifiers-implementation.html#Qualifiers-implementation">Qualifiers implementation</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Declarators-implementation.html#Declarators-implementation">Declarators implementation</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Statements-implementation.html#Statements-implementation">Statements implementation</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Preprocessing-directives-implementation.html#Preprocessing-directives-implementation">Preprocessing directives implementation</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Library-functions-implementation.html#Library-functions-implementation">Library functions implementation</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Architecture-implementation.html#Architecture-implementation">Architecture implementation</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Locale_002dspecific-behavior-implementation.html#Locale_002dspecific-behavior-implementation">Locale-specific behavior implementation</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
</table>

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<p>
Next: <a href="C_002b_002b-Implementation.html#C_002b_002b-Implementation" accesskey="n" rel="next">C++ Implementation</a>, Previous: <a href="Invoking-GCC.html#Invoking-GCC" accesskey="p" rel="prev">Invoking 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>
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