Alternate-Keywords.html 5.4 KB

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  68. <a name="Alternate-Keywords-1"></a>
  69. <h3 class="section">6.46 Alternate Keywords</h3>
  70. <a name="index-alternate-keywords"></a>
  71. <a name="index-keywords_002c-alternate"></a>
  72. <p><samp>-ansi</samp> and the various <samp>-std</samp> options disable certain
  73. keywords. This causes trouble when you want to use GNU C extensions, or
  74. a general-purpose header file that should be usable by all programs,
  75. including ISO C programs. The keywords <code>asm</code>, <code>typeof</code> and
  76. <code>inline</code> are not available in programs compiled with
  77. <samp>-ansi</samp> or <samp>-std</samp> (although <code>inline</code> can be used in a
  78. program compiled with <samp>-std=c99</samp> or <samp>-std=c11</samp>). The
  79. ISO C99 keyword
  80. <code>restrict</code> is only available when <samp>-std=gnu99</samp> (which will
  81. eventually be the default) or <samp>-std=c99</samp> (or the equivalent
  82. <samp>-std=iso9899:1999</samp>), or an option for a later standard
  83. version, is used.
  84. </p>
  85. <p>The way to solve these problems is to put &lsquo;<samp>__</samp>&rsquo; at the beginning and
  86. end of each problematical keyword. For example, use <code>__asm__</code>
  87. instead of <code>asm</code>, and <code>__inline__</code> instead of <code>inline</code>.
  88. </p>
  89. <p>Other C compilers won&rsquo;t accept these alternative keywords; if you want to
  90. compile with another compiler, you can define the alternate keywords as
  91. macros to replace them with the customary keywords. It looks like this:
  92. </p>
  93. <div class="smallexample">
  94. <pre class="smallexample">#ifndef __GNUC__
  95. #define __asm__ asm
  96. #endif
  97. </pre></div>
  98. <a name="index-_005f_005fextension_005f_005f"></a>
  99. <a name="index-pedantic-3"></a>
  100. <p><samp>-pedantic</samp> and other options cause warnings for many GNU C extensions.
  101. You can
  102. prevent such warnings within one expression by writing
  103. <code>__extension__</code> before the expression. <code>__extension__</code> has no
  104. effect aside from this.
  105. </p>
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