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117 lines
4.6 KiB
HTML
117 lines
4.6 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) 1988-2018 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; with the
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Invariant Sections being "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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"GNU Free Documentation License".
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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>Conditionals (Using the GNU Compiler Collection (GCC))</title>
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<meta name="description" content="Conditionals (Using the GNU Compiler Collection (GCC))">
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<meta name="keywords" content="Conditionals (Using the GNU Compiler Collection (GCC))">
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<meta name="resource-type" content="document">
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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="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="C-Extensions.html#C-Extensions" rel="up" title="C Extensions">
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<link href="_005f_005fint128.html#g_t_005f_005fint128" rel="next" title="__int128">
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<link href="Typeof.html#Typeof" rel="prev" title="Typeof">
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</style>
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</head>
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<body lang="en">
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<a name="Conditionals"></a>
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<div class="header">
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<p>
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Next: <a href="_005f_005fint128.html#g_t_005f_005fint128" accesskey="n" rel="next">__int128</a>, Previous: <a href="Typeof.html#Typeof" accesskey="p" rel="prev">Typeof</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Conditionals-with-Omitted-Operands"></a>
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<h3 class="section">6.7 Conditionals with Omitted Operands</h3>
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<a name="index-conditional-expressions_002c-extensions"></a>
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<a name="index-omitted-middle_002doperands"></a>
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<a name="index-middle_002doperands_002c-omitted"></a>
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<a name="index-extensions_002c-_003f_003a"></a>
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<a name="index-_003f_003a-extensions"></a>
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<p>The middle operand in a conditional expression may be omitted. Then
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if the first operand is nonzero, its value is the value of the conditional
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expression.
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</p>
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<p>Therefore, the expression
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</p>
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<div class="smallexample">
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<pre class="smallexample">x ? : y
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</pre></div>
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<p>has the value of <code>x</code> if that is nonzero; otherwise, the value of
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<code>y</code>.
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</p>
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<p>This example is perfectly equivalent to
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</p>
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<div class="smallexample">
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<pre class="smallexample">x ? x : y
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</pre></div>
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<a name="index-side-effect-in-_003f_003a"></a>
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<a name="index-_003f_003a-side-effect"></a>
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<p>In this simple case, the ability to omit the middle operand is not
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especially useful. When it becomes useful is when the first operand does,
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or may (if it is a macro argument), contain a side effect. Then repeating
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the operand in the middle would perform the side effect twice. Omitting
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the middle operand uses the value already computed without the undesirable
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effects of recomputing it.
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</p>
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</body>
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</html>
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