📄 malloc2.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!-- but may not be published or retransmitted without explicit permission.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 malloc.sgml dated Wed Dec 21 13:50:44 2005 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/malloc/malloc2.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:49 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 7.2</title><link href="malloc1.html" rev=precedes><link href="attitude.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="malloc1.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="attitude.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 7.2</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>I can't get <TT>strcat</TT> to work.I tried<pre> char *s1 = "Hello, "; char *s2 = "world!"; char *s3 = strcat(s1, s2);</pre>but I got strange results.</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>As in question <a href="malloc1.html">7.1</a>,the main problem hereis that space for the concatenated result isnot properly allocated.C does not provide an automatically-managed string type.C compilers allocate memoryonly for objects explicitlymentioned in the source code(in the case of strings,thisincludes character arrays and string literals).The programmer mustarrangefor sufficient space forthe results of run-time operations such as string concatenation,typically by declaring arrays, or by calling <TT>malloc</TT>.</p><p><TT>strcat</TT> performs no allocation;the second string is appended to the first one,in place.The first(destination)string mustbe writable andhave enough roomfor the concatenated result.Therefore, one fix would be to declare the first string asanarray:<pre> char s1[20] = "Hello, ";</pre>(In production code,of course,we wouldn't use magic numbers like ``20'';we'd use more robust mechanismsto guarantee sufficient space.)</p><p>Since <TT>strcat</TT>returns the value of its first argument(<TT>s1</TT>, in this case),the variable <TT>s3</TT>inthe question aboveissuperfluous;after the call to <TT>strcat</TT>,<TT>s1</TT> contains the result.</p><p>The original call to <TT>strcat</TT> in the questionactually hastwo problems:the string literal pointed to by <TT>s1</TT>,besides not being big enough for any concatenated text,is not necessarily writableat all.See question<a href="../decl/strlitinit.html">1.32</a>.</p><p>References:CT&P Sec. 3.2 p. 32<br></p><!-- aend --><p><hr><a href="malloc1.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="attitude.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/malloc/malloc2.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:49 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 + -