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<html lang="en"><head><title>Using the GNU Compiler Collection (GCC)</title><meta http-equiv="Content-Type" content="text/html"><meta name="description" content="Using the GNU Compiler Collection (GCC)"><meta name="generator" content="makeinfo 4.6"><!--Copyright © 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,1999, 2000, 2001, 2002, 2003, 2004 Free Software Foundation, Inc. <p>Permission is granted to copy, distribute and/or modify this documentunder the terms of the GNU Free Documentation License, Version 1.2 orany later version published by the Free Software Foundation; with theInvariant Sections being "GNU General Public License" and "FundingFree Software", the Front-Cover texts being (a) (see below), and withthe Back-Cover Texts being (b) (see below). A copy of the license isincluded in the section entitled "GNU Free Documentation License". <p>(a) The FSF's Front-Cover Text is: <p>A GNU Manual <p>(b) The FSF's Back-Cover Text is: <p>You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development.--><meta http-equiv="Content-Style-Type" content="text/css"><style type="text/css"><!-- pre.display { font-family:inherit } pre.format { font-family:inherit } pre.smalldisplay { font-family:inherit; font-size:smaller } pre.smallformat { font-family:inherit; font-size:smaller } pre.smallexample { font-size:smaller } pre.smalllisp { font-size:smaller }--></style></head><body><div class="node"><p>Node: <a name="Conditionals">Conditionals</a>,Next: <a rel="next" accesskey="n" href="Long-Long.html#Long%20Long">Long Long</a>,Previous: <a rel="previous" accesskey="p" href="Typeof.html#Typeof">Typeof</a>,Up: <a rel="up" accesskey="u" href="C-Extensions.html#C%20Extensions">C Extensions</a><hr><br></div><h3 class="section">Conditionals with Omitted Operands</h3><p>The middle operand in a conditional expression may be omitted. Thenif the first operand is nonzero, its value is the value of the conditionalexpression. <p>Therefore, the expression<pre class="smallexample"> x ? : y </pre><p>has the value of <code>x</code> if that is nonzero; otherwise, the value of<code>y</code>. <p>This example is perfectly equivalent to<pre class="smallexample"> x ? x : y </pre><p>In this simple case, the ability to omit the middle operand is notespecially useful. When it becomes useful is when the first operand does,or may (if it is a macro argument), contain a side effect. Then repeatingthe operand in the middle would perform the side effect twice. Omittingthe middle operand uses the value already computed without the undesirableeffects of recomputing it. </body></html>⌨️ 快捷键说明
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