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129 lines
5.0 KiB
HTML
129 lines
5.0 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1987-2018 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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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Elif (The C Preprocessor)</title>
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<meta name="description" content="Elif (The C Preprocessor)">
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<meta name="keywords" content="Elif (The C Preprocessor)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Index-of-Directives.html#Index-of-Directives" rel="index" title="Index of Directives">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Conditional-Syntax.html#Conditional-Syntax" rel="up" title="Conditional Syntax">
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<link href="Deleted-Code.html#Deleted-Code" rel="next" title="Deleted Code">
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<link href="Else.html#Else" rel="prev" title="Else">
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<style type="text/css">
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<!--
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a.summary-letter {text-decoration: none}
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blockquote.indentedblock {margin-right: 0em}
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blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
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blockquote.smallquotation {font-size: smaller}
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div.display {margin-left: 3.2em}
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div.example {margin-left: 3.2em}
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div.lisp {margin-left: 3.2em}
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div.smalldisplay {margin-left: 3.2em}
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div.smallexample {margin-left: 3.2em}
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div.smalllisp {margin-left: 3.2em}
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kbd {font-style: oblique}
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pre.display {font-family: inherit}
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pre.format {font-family: inherit}
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pre.menu-comment {font-family: serif}
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pre.menu-preformatted {font-family: serif}
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pre.smalldisplay {font-family: inherit; font-size: smaller}
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pre.smallexample {font-size: smaller}
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pre.smallformat {font-family: inherit; font-size: smaller}
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pre.smalllisp {font-size: smaller}
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span.nolinebreak {white-space: nowrap}
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span.roman {font-family: initial; font-weight: normal}
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span.sansserif {font-family: sans-serif; font-weight: normal}
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ul.no-bullet {list-style: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Elif"></a>
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<div class="header">
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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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</div>
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<hr>
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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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</p>
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</body>
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</html>
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