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  20. <title>Alternate Keywords (Using the GNU Compiler Collection (GCC))</title>
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  67. <a name="Alternate-Keywords-1"></a>
  68. <h3 class="section">6.48 Alternate Keywords</h3>
  69. <a name="index-alternate-keywords"></a>
  70. <a name="index-keywords_002c-alternate"></a>
  71. <p><samp>-ansi</samp> and the various <samp>-std</samp> options disable certain
  72. keywords. This causes trouble when you want to use GNU C extensions, or
  73. a general-purpose header file that should be usable by all programs,
  74. including ISO C programs. The keywords <code>asm</code>, <code>typeof</code> and
  75. <code>inline</code> are not available in programs compiled with
  76. <samp>-ansi</samp> or <samp>-std</samp> (although <code>inline</code> can be used in a
  77. program compiled with <samp>-std=c99</samp> or a later standard). The
  78. ISO C99 keyword
  79. <code>restrict</code> is only available when <samp>-std=gnu99</samp> (which will
  80. eventually be the default) or <samp>-std=c99</samp> (or the equivalent
  81. <samp>-std=iso9899:1999</samp>), or an option for a later standard
  82. version, is used.
  83. </p>
  84. <p>The way to solve these problems is to put &lsquo;<samp>__</samp>&rsquo; at the beginning and
  85. end of each problematical keyword. For example, use <code>__asm__</code>
  86. instead of <code>asm</code>, and <code>__inline__</code> instead of <code>inline</code>.
  87. </p>
  88. <p>Other C compilers won&rsquo;t accept these alternative keywords; if you want to
  89. compile with another compiler, you can define the alternate keywords as
  90. macros to replace them with the customary keywords. It looks like this:
  91. </p>
  92. <div class="smallexample">
  93. <pre class="smallexample">#ifndef __GNUC__
  94. #define __asm__ asm
  95. #endif
  96. </pre></div>
  97. <a name="index-_005f_005fextension_005f_005f"></a>
  98. <a name="index-pedantic-3"></a>
  99. <p><samp>-pedantic</samp> and other options cause warnings for many GNU C extensions.
  100. You can
  101. prevent such warnings within one expression by writing
  102. <code>__extension__</code> before the expression. <code>__extension__</code> has no
  103. effect aside from this.
  104. </p>
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