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<h3 class="section">6.44 Alternate Keywords</h3>
<p><a name="index-alternate-keywords-3507"></a><a name="index-keywords_002c-alternate-3508"></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> or <samp><span class="option">-std=c11</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>), or an option for a later standard
version, is used.
<p>The way to solve these problems is to put ‘<samp><span class="samp">__</span></samp>’ 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-3509"></a><a name="index-pedantic-3510"></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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