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<a name="isdigit_002c-isdigit_005fl_002d_002d_002ddecimal-digit-predicate"></a>
<h3 class="section">3.6 <code>isdigit</code>, <code>isdigit_l</code>&mdash;decimal digit predicate</h3>
<a name="index-isdigit"></a>
<a name="index-isdigit_005fl"></a>
<p><strong>Synopsis</strong>
</p><div class="example">
<pre class="example">#include &lt;ctype.h&gt;
int isdigit(int <var>c</var>);

#include &lt;ctype.h&gt;
int isdigit_l(int <var>c</var>, locale_t <var>locale</var>);

</pre></div>
<p><strong>Description</strong><br>
<code>isdigit</code> is a macro which classifies singlebyte charset values by table
lookup.  It is a predicate returning non-zero for decimal digits, and 0 for
other characters.  It is defined only if <var>c</var> is representable as an
unsigned char or if <var>c</var> is EOF.
</p>
<p><code>isdigit_l</code> is like <code>isdigit</code> but performs the check based on the
locale specified by the locale object locale.  If <var>locale</var> is
LC_GLOBAL_LOCALE or not a valid locale object, the behaviour is undefined.
</p>
<p>You can use a compiled subroutine instead of the macro definition by
undefining the macro using &lsquo;<code>#undef isdigit</code>&rsquo; or &lsquo;<code>#undef isdigit_l</code>&rsquo;.
</p>
<br>
<p><strong>Returns</strong><br>
<code>isdigit</code>, <code>isdigit_l</code> return non-zero if <var>c</var> is a decimal digit
(<code>0</code>&ndash;<code>9</code>).
</p>
<br>
<p><strong>Portability</strong><br>
<code>isdigit</code> is ANSI C.
<code>isdigit_l</code> is POSIX-1.2008.
</p>
<p>No supporting OS subroutines are required.
</p>
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