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<title>Using the GNU Compiler Collection (GCC): Alternate Keywords</title>

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<a name="Alternate-Keywords"></a>
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<a name="Alternate-Keywords-1"></a>
<h3 class="section">6.44 Alternate Keywords</h3>
<a name="index-alternate-keywords"></a>
<a name="index-keywords_002c-alternate"></a>

<p><samp>-ansi</samp> and the various <samp>-std</samp> options disable certain
keywords.  This causes trouble when you want to use GNU C extensions, or
a general-purpose header file that should be usable by all programs,
including ISO C programs.  The keywords <code>asm</code>, <code>typeof</code> and
<code>inline</code> are not available in programs compiled with
<samp>-ansi</samp> or <samp>-std</samp> (although <code>inline</code> can be used in a
program compiled with <samp>-std=c99</samp> or <samp>-std=c11</samp>).  The
ISO C99 keyword
<code>restrict</code> is only available when <samp>-std=gnu99</samp> (which will
eventually be the default) or <samp>-std=c99</samp> (or the equivalent
<samp>-std=iso9899:1999</samp>), or an option for a later standard
version, is used.
</p>
<p>The way to solve these problems is to put &lsquo;<samp>__</samp>&rsquo; at the beginning and
end of each problematical keyword.  For example, use <code>__asm__</code>
instead of <code>asm</code>, and <code>__inline__</code> instead of <code>inline</code>.
</p>
<p>Other C compilers won&rsquo;t accept these alternative keywords; if you want to
compile with another compiler, you can define the alternate keywords as
macros to replace them with the customary keywords.  It looks like this:
</p>
<div class="smallexample">
<pre class="smallexample">#ifndef __GNUC__
#define __asm__ asm
#endif
</pre></div>

<a name="index-_005f_005fextension_005f_005f"></a>
<a name="index-pedantic-4"></a>
<p><samp>-pedantic</samp> and other options cause warnings for many GNU C extensions.
You can
prevent such warnings within one expression by writing
<code>__extension__</code> before the expression.  <code>__extension__</code> has no
effect aside from this.
</p>


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