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<a name="isalnum_002c-isalnum_005fl_002d_002d_002dalphanumeric-character-predicate"></a>
<h3 class="section">3.1 <code>isalnum</code>, <code>isalnum_l</code>&mdash;alphanumeric character predicate</h3>
<a name="index-isalnum"></a>
<a name="index-isalnum_005fl"></a>
<p><strong>Synopsis</strong>
</p><div class="example">
<pre class="example">#include &lt;ctype.h&gt;
int isalnum(int <var>c</var>);

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

</pre></div>
<p><strong>Description</strong><br>
<code>isalnum</code> is a macro which classifies singlebyte charset values by table
lookup.  It is a predicate returning non-zero for alphabetic or
numeric ASCII characters, and <code>0</code> for other arguments.  It is defined
only if <var>c</var> is representable as an unsigned char or if <var>c</var> is EOF.
</p>
<p><code>isalnum_l</code> is like <code>isalnum</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 isalnum</code>&rsquo; or &lsquo;<code>#undef isalnum_l</code>&rsquo;.
</p>
<br>
<p><strong>Returns</strong><br>
<code>isalnum</code>,<code>isalnum_l</code> return non-zero if <var>c</var> is a letter or a digit.
</p>
<br>
<p><strong>Portability</strong><br>
<code>isalnum</code> is ANSI C.
<code>isalnum_l</code> is POSIX-1.2008.
</p>
<p>No OS subroutines are required.
</p>
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