📄 shortcircuit.html
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<!DOCTYPE HTML PUBLIC "-//W3O//DTD W3 HTML 2.0//EN"><!-- This collection of hypertext pages is Copyright 1995-2005 by Steve Summit. --><!-- Content from the book "C Programming FAQs: Frequently Asked Questions" --><!-- (Addison-Wesley, 1995, ISBN 0-201-84519-9) is made available here by --><!-- permission of the author and the publisher as a service to the community. --><!-- It is intended to complement the use of the published text --><!-- and is protected by international copyright laws. --><!-- The on-line content may be accessed freely for personal use --><!-- but may not be published or retransmitted without explicit permission. --><!-- --><!-- this page built Sat Dec 24 21:47:45 2005 by faqproc version 2.7 --><!-- from source file expr.sgml dated Sat Jul 3 17:10:33 2004 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/expr/shortcircuit.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:47 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 3.6</title><link href="seqpointops.html" rev=precedes><link href="comma.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="seqpointops.html" rev=precedes><img src="../images/buttonleft.gif" alt="prev"></a><a href="index.html" rev=subdocument><img src="../images/buttonup.gif" alt="up"></a><a href="comma.html" rel=precedes><img src="../images/buttonright.gif" alt="next"></a> <a href="../index-2.html"><img src="../images/buttontop.gif" alt="top/contents"></a><a href="../search.html"><img src="../images/buttonsrch.gif" alt="search"></a><hr><p><!-- qbegin --><h1>comp.lang.c FAQ list<font color=blue>·</font><!-- qtag -->Question 3.6</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>Is it safe to assumethat the right-hand sideof the<TT>&&</TT>and<TT>||</TT>operatorswon't be evaluatedif the left-hand side determines the outcome?</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>Yes.Idioms like<pre> if(d != 0 && n / d > 0) { /* average is greater than 0 */ }</pre>and<pre> if(p == NULL || *p == '\0') { /* no string */ }</pre>are quite common in C,and depend onthis so-called short-circuiting behavior.In the first example,in the absence of short-circuiting behavior,the right-hand side would divide by 0--and perhaps crash--if<TT>d</TT> were equal to 0.In the second example,the right-hand side would attempt to referencenonexistent memory--and perhaps crash--if<TT>p</TT> were a null pointer.</p><p>References:ISO Sec. 6.3.13, Sec. 6.3.14<br>H&S Sec. 7.7 pp. 217-8<br></p><!-- aend --><p><hr><a href="seqpointops.html" rev=precedes><img src="../images/buttonleft.gif" alt="prev"></a><a href="index.html" rev=subdocument><img src="../images/buttonup.gif" alt="up"></a><a href="comma.html" rel=precedes><img src="../images/buttonright.gif" alt="next"></a> <a href="../questions.html"><img src="../images/buttontop.gif" alt="contents"></a><a href="../search.html"><img src="../images/buttonsrch.gif" alt="search"></a><br><!-- lastfooter --><a href="../about.html">about this FAQ list</a> <a href="../eskimo.html">about eskimo</a> <a href="../search.html">search</a> <a href="../feedback.html">feedback</a> <a href="copyright.html">copyright</a><p>Hosted by<a href="http://www.eskimo.com/"><img src="../../www.eskimo.com/img/link/eskitiny.gif" alt="Eskimo North"></a></body><!-- Mirrored from c-faq.com/expr/shortcircuit.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:47 GMT --></html>⌨️ 快捷键说明
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