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<a name="g_t_005f_005fhas_005fbuiltin-1"></a>
<h4 class="subsection">4.2.8 <code>__has_builtin</code></h4>
<a name="index-_005f_005fhas_005fbuiltin"></a>

<p>The special operator <code>__has_builtin (<var>operand</var>)</code> may be used in
constant integer contexts and in preprocessor &lsquo;<samp>#if</samp>&rsquo; and &lsquo;<samp>#elif</samp>&rsquo;
expressions to test whether the symbol named by its <var>operand</var> is
recognized as a built-in function by GCC in the current language and
conformance mode.  It evaluates to a constant integer with a nonzero
value if the argument refers to such a function, and to zero otherwise.
The operator may also be used in preprocessor &lsquo;<samp>#if</samp>&rsquo; and &lsquo;<samp>#elif</samp>&rsquo;
expressions.  The <code>__has_builtin</code> operator by itself, without any
<var>operand</var> or parentheses, acts as a predefined macro so that support
for it can be tested in portable code.  Thus, the recommended use of
the operator is as follows:
</p>
<div class="smallexample">
<pre class="smallexample">#if defined __has_builtin
#  if __has_builtin (__builtin_object_size)
#    define builtin_object_size(ptr) __builtin_object_size (ptr, 2)
#  endif
#endif
#ifndef builtin_object_size
#  define builtin_object_size(ptr)   ((size_t)-1)
#endif
</pre></div>


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