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<title>The C Preprocessor: __has_builtin</title>
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Next: <a href="_005f_005fhas_005finclude.html#g_t_005f_005fhas_005finclude" accesskey="n" rel="next"><code>__has_include</code></a>, Previous: <a href="_005f_005fhas_005fc_005fattribute.html#g_t_005f_005fhas_005fc_005fattribute" accesskey="p" rel="previous"><code>__has_c_attribute</code></a>, Up: <a href="Conditional-Syntax.html#Conditional-Syntax" accesskey="u" rel="up">Conditional Syntax</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p>
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<h4 class="subsection">4.2.9 <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 ‘<samp>#if</samp>’ and ‘<samp>#elif</samp>’
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 ‘<samp>#if</samp>’ and ‘<samp>#elif</samp>’
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
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