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