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<title>The C Preprocessor: Elif</title>
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<p>
Next: <a href="_005f_005fhas_005fattribute.html#g_t_005f_005fhas_005fattribute" accesskey="n" rel="next"><code>__has_attribute</code></a>, Previous: <a href="Else.html#Else" accesskey="p" rel="previous">Else</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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<a name="Elif-1"></a>
<h4 class="subsection">4.2.5 Elif</h4>
<a name="index-_0023elif"></a>
<p>One common case of nested conditionals is used to check for more than two
possible alternatives. For example, you might have
</p>
<div class="smallexample">
<pre class="smallexample">#if X == 1
…
#else /* X != 1 */
#if X == 2
…
#else /* X != 2 */
…
#endif /* X != 2 */
#endif /* X != 1 */
</pre></div>
<p>Another conditional directive, ‘<samp>#elif</samp>’, allows this to be
abbreviated as follows:
</p>
<div class="smallexample">
<pre class="smallexample">#if X == 1
…
#elif X == 2
…
#else /* X != 2 and X != 1*/
…
#endif /* X != 2 and X != 1*/
</pre></div>
<p>‘<samp>#elif</samp>’ stands for “else if”. Like ‘<samp>#else</samp>’, it goes in the
middle of a conditional group and subdivides it; it does not require a
matching ‘<samp>#endif</samp>’ of its own. Like ‘<samp>#if</samp>’, the ‘<samp>#elif</samp>’
directive includes an expression to be tested. The text following the
‘<samp>#elif</samp>’ is processed only if the original ‘<samp>#if</samp>’-condition
failed and the ‘<samp>#elif</samp>’ condition succeeds.
</p>
<p>More than one ‘<samp>#elif</samp>’ can go in the same conditional group. Then
the text after each ‘<samp>#elif</samp>’ is processed only if the ‘<samp>#elif</samp>’
condition succeeds after the original ‘<samp>#if</samp>’ and all previous
‘<samp>#elif</samp>’ directives within it have failed.
</p>
<p>‘<samp>#else</samp>’ is allowed after any number of ‘<samp>#elif</samp>’ directives, but
‘<samp>#elif</samp>’ may not follow ‘<samp>#else</samp>’.
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