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98 lines
4.3 KiB
HTML
98 lines
4.3 KiB
HTML
4 years ago
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<html lang="en">
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<head>
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<title>Elif - The C Preprocessor</title>
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<meta http-equiv="Content-Type" content="text/html">
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<meta name="description" content="The C Preprocessor">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Conditional-Syntax.html#Conditional-Syntax" title="Conditional Syntax">
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<link rel="prev" href="Else.html#Else" title="Else">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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Copyright (C) 1987-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation. A copy of
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the license is included in the
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section entitled ``GNU Free Documentation License''.
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This manual contains no Invariant Sections. The Front-Cover Texts are
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(a) (see below), and the Back-Cover Texts are (b) (see below).
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development.
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-->
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<meta http-equiv="Content-Style-Type" content="text/css">
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<style type="text/css"><!--
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pre.display { font-family:inherit }
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pre.format { font-family:inherit }
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pre.smalldisplay { font-family:inherit; font-size:smaller }
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pre.smallformat { font-family:inherit; font-size:smaller }
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pre.smallexample { font-size:smaller }
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pre.smalllisp { font-size:smaller }
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span.sc { font-variant:small-caps }
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span.roman { font-family:serif; font-weight:normal; }
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span.sansserif { font-family:sans-serif; font-weight:normal; }
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--></style>
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</head>
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<body>
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<div class="node">
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<a name="Elif"></a>
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<p>
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Previous: <a rel="previous" accesskey="p" href="Else.html#Else">Else</a>,
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Up: <a rel="up" accesskey="u" href="Conditional-Syntax.html#Conditional-Syntax">Conditional Syntax</a>
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<hr>
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</div>
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<h4 class="subsection">4.2.5 Elif</h4>
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<p><a name="index-g_t_0023elif-91"></a>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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<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>
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<p>Another conditional directive, ‘<samp><span class="samp">#elif</span></samp>’, allows this to be
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abbreviated as follows:
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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>
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<p>‘<samp><span class="samp">#elif</span></samp>’ stands for “else if”. Like ‘<samp><span class="samp">#else</span></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><span class="samp">#endif</span></samp>’ of its own. Like ‘<samp><span class="samp">#if</span></samp>’, the ‘<samp><span class="samp">#elif</span></samp>’
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directive includes an expression to be tested. The text following the
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‘<samp><span class="samp">#elif</span></samp>’ is processed only if the original ‘<samp><span class="samp">#if</span></samp>’-condition
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failed and the ‘<samp><span class="samp">#elif</span></samp>’ condition succeeds.
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<p>More than one ‘<samp><span class="samp">#elif</span></samp>’ can go in the same conditional group. Then
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the text after each ‘<samp><span class="samp">#elif</span></samp>’ is processed only if the ‘<samp><span class="samp">#elif</span></samp>’
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condition succeeds after the original ‘<samp><span class="samp">#if</span></samp>’ and all previous
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‘<samp><span class="samp">#elif</span></samp>’ directives within it have failed.
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<p>‘<samp><span class="samp">#else</span></samp>’ is allowed after any number of ‘<samp><span class="samp">#elif</span></samp>’ directives, but
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‘<samp><span class="samp">#elif</span></samp>’ may not follow ‘<samp><span class="samp">#else</span></samp>’.
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</body></html>
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