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<title>Using the GNU Compiler Collection (GCC): Library functions implementation</title>

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<a name="Library-Functions"></a>
<h3 class="section">4.14 Library Functions</h3>

<p>The behavior of most of these points are dependent on the implementation
of the C library, and are not defined by GCC itself.
</p>
<ul>
<li> <cite>The null pointer constant to which the macro <code>NULL</code> expands
(C90 7.1.6, C99 7.17, C11 7.19).</cite>

<p>In <code>&lt;stddef.h&gt;</code>, <code>NULL</code> expands to <code>((void *)0)</code>.  GCC
does not provide the other headers which define <code>NULL</code> and some
library implementations may use other definitions in those headers.
</p>
</li></ul>


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