📄 index.html
字号:
<!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!-- but may not be published or retransmitted without explicit permission.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/index.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:54:12 GMT --><head><meta name=GENERATOR content="faqproc"><title>Expressions</title></head><body bgcolor="#ffffff"> <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><H1>3. Expressions</H1><p><a href="evalorder1.html" rel=subdocument>3.1</a>Why doesn'tthis code:<pre>a[i] = i++;</pre>work?</p><p><a href="evalorder2.html" rel=subdocument>3.2</a>Under my compiler, the code<pre>int i = 7;printf("%d\n", i++ * i++);</pre>prints 49.Regardless of the order of evaluation, shouldn't it print 56?</p><p><a href="ieqiplusplus.html" rel=subdocument>3.3</a>I've experimented withthe code<pre>int i = 3;i = i++;</pre>on several compilers.Some gave <TT>i</TT> thevalue 3,andsome gave 4.Which compiler is correct?</p><p><a href="xorswapexpr.html" rel=subdocument>3.3b</a>Here's a slick expression:<pre>a ^= b ^= a ^= b</pre>It swaps <TT>a</TT> and <TT>b</TT> without using a temporary.</p><p><a href="precvsooe.html" rel=subdocument>3.4</a>Can I use explicit parentheses to forcethe order of evaluation I want,and control these side effects?Even if I don't, doesn't precedence dictate it?</p><p><a href="seqpointops.html" rel=subdocument>3.5</a>But what about the<TT>&&</TT>and<TT>||</TT>operators?<br>I see code like ``<TT>while((c = getchar()) != EOF && c != '\n')</TT>'' ...</p><p><a href="shortcircuit.html" rel=subdocument>3.6</a>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><a href="comma.html" rel=subdocument>3.7</a>Why did<pre>printf("%d %d", f1(), f2());</pre>call <TT>f2</TT> first?I thought the comma operator guaranteed left-to-right evaluation.</p><p><a href="seqpoints.html" rel=subdocument>3.8</a>How can I understandcomplex expressions like the ones in this section,and avoid writing undefined ones?What's a ``sequence point''?</p><p><a href="evalorder4.html" rel=subdocument>3.9</a>Soif I write<pre>a[i] = i++;</pre>and I don't carewhich cell of <TT>a[]</TT> gets written to,the code is fine,and <TT>i</TT> getsincremented by one,right?</p><p><a href="experiment.html" rel=subdocument>3.10a</a>People keep saying that the behaviorof <TT>i = i++</TT>is undefined,butI just triediton an ANSI-conforming compiler,and got the results I expected.</p><p><a href="expec0.html" rel=subdocument>3.10b</a>People told me that if I evaluated an undefined expression,or accessed an uninitialized variable,I'd get a random, garbage value.But I tried it, and got <em>zero</em>.What's up with that?</p><p><a href="confused.html" rel=subdocument>3.11</a>How can I avoid these undefined evaluation order difficultiesif I don't feel like learning the complicated rules?</p><p><a href="prevspost.html" rel=subdocument>3.12a</a>What's the difference between <TT>++i</TT> and <TT>i++</TT>?</p><p><a href="plusplus.html" rel=subdocument>3.12b</a>If I'm not using the value of the expression,should I use <TT>++i</TT> or <TT>i++</TT> to increment a variable?</p><p><a href="transitivity.html" rel=subdocument>3.13</a>I need to check whether one number lies between two others.Why doesn't<pre>if(a < b < c)</pre>work?</p><p><a href="intoverflow1.html" rel=subdocument>3.14</a>Why doesn't the code<pre>int a = 1000, b = 1000;long int c = a * b;</pre>work?</p><p><a href="intovf3.html" rel=subdocument>3.14b</a>How can I ensure that integer arithmetic doesn't overflow?</p><p><a href="truncation1.html" rel=subdocument>3.15</a>Why does the code<pre>double degC, degF;degC = 5 / 9 * (degF - 32);</pre>keep giving me 0?</p><p><a href="qcolonlhs.html" rel=subdocument>3.16</a>I have a complicated expression whichI haveto assignto one of two variables,depending on a condition.Can I use code like this?<pre> ((condition) ? a : b) = complicated_expression;</pre></p><p><a href="ternprec.html" rel=subdocument>3.17</a>I havesome codecontaining expressionslike<pre>a ? b = c : d</pre>and some compilers are accepting it but some are not.</p><p><a href="unswarn.html" rel=subdocument>3.18</a>What does the warning``semantics of `<TT>></TT>' change in ANSI C''mean?</p><p><a href="preservingrules.html" rel=subdocument>3.19</a>What's the difference between the ``unsigned preserving''and ``value preserving'' rules?</p><hr><p><a href="../index-2.html">top</a></p><p><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><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></p></body><!-- Mirrored from c-faq.com/expr/index.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:54:22 GMT --></html>⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -