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| <title>Using the GNU Compiler Collection (GCC): Alternate Keywords</title> |
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| <a name="Alternate-Keywords-1"></a> |
| <h3 class="section">6.45 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 ‘<samp>__</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> |
| <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: |
| </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. |
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