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<h3 class="section">6.43 Alternate Keywords</h3>

<p><a name="index-alternate-keywords-2601"></a><a name="index-keywords_002c-alternate-2602"></a>
<samp><span class="option">-ansi</span></samp> and the various <samp><span class="option">-std</span></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><span class="option">-ansi</span></samp> or <samp><span class="option">-std</span></samp> (although <code>inline</code> can be used in a
program compiled with <samp><span class="option">-std=c99</span></samp>).  The ISO C99 keyword
<code>restrict</code> is only available when <samp><span class="option">-std=gnu99</span></samp> (which will
eventually be the default) or <samp><span class="option">-std=c99</span></samp> (or the equivalent
<samp><span class="option">-std=iso9899:1999</span></samp>) is used.

 <p>The way to solve these problems is to put &lsquo;<samp><span class="samp">__</span></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>Other C compilers won'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:

<pre class="smallexample">     #ifndef __GNUC__
     #define __asm__ asm
     #endif
</pre>
 <p><a name="index-g_t_005f_005fextension_005f_005f-2603"></a><a name="index-pedantic-2604"></a><samp><span class="option">-pedantic</span></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.

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