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| <title>The C Preprocessor: Elif</title> |
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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> |
| <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> |
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| ‘<samp>#elif</samp>’ may not follow ‘<samp>#else</samp>’. |
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