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91 lines
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91 lines
4.6 KiB
HTML
4 years ago
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<title>Alternate Keywords - Using the GNU Compiler Collection (GCC)</title>
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<link rel="up" href="C-Extensions.html#C-Extensions" title="C Extensions">
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<link rel="prev" href="Using-Assembly-Language-with-C.html#Using-Assembly-Language-with-C" title="Using Assembly Language with C">
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<a name="Alternate-Keywords"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Incomplete-Enums.html#Incomplete-Enums">Incomplete Enums</a>,
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Previous: <a rel="previous" accesskey="p" href="Using-Assembly-Language-with-C.html#Using-Assembly-Language-with-C">Using Assembly Language with C</a>,
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Up: <a rel="up" accesskey="u" href="C-Extensions.html#C-Extensions">C Extensions</a>
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<hr>
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</div>
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<h3 class="section">6.44 Alternate Keywords</h3>
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<p><a name="index-alternate-keywords-3507"></a><a name="index-keywords_002c-alternate-3508"></a>
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<samp><span class="option">-ansi</span></samp> and the various <samp><span class="option">-std</span></samp> options disable certain
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keywords. This causes trouble when you want to use GNU C extensions, or
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a general-purpose header file that should be usable by all programs,
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including ISO C programs. The keywords <code>asm</code>, <code>typeof</code> and
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<code>inline</code> are not available in programs compiled with
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<samp><span class="option">-ansi</span></samp> or <samp><span class="option">-std</span></samp> (although <code>inline</code> can be used in a
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program compiled with <samp><span class="option">-std=c99</span></samp> or <samp><span class="option">-std=c11</span></samp>). The
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ISO C99 keyword
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<code>restrict</code> is only available when <samp><span class="option">-std=gnu99</span></samp> (which will
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eventually be the default) or <samp><span class="option">-std=c99</span></samp> (or the equivalent
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<samp><span class="option">-std=iso9899:1999</span></samp>), or an option for a later standard
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version, is used.
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<p>The way to solve these problems is to put ‘<samp><span class="samp">__</span></samp>’ at the beginning and
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end of each problematical keyword. For example, use <code>__asm__</code>
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instead of <code>asm</code>, and <code>__inline__</code> instead of <code>inline</code>.
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<p>Other C compilers won't accept these alternative keywords; if you want to
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compile with another compiler, you can define the alternate keywords as
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macros to replace them with the customary keywords. It looks like this:
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<pre class="smallexample"> #ifndef __GNUC__
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#define __asm__ asm
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#endif
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</pre>
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<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.
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You can
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prevent such warnings within one expression by writing
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<code>__extension__</code> before the expression. <code>__extension__</code> has no
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effect aside from this.
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</body></html>
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