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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!-- but may not be published or retransmitted without explicit permission.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 pointers.sgml dated Wed Dec 21 13:07:10 2005 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/ptrs/explscale.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 4.4</title><link href="unopprec2.html" rev=precedes><link href="castincr.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="unopprec2.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="castincr.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 4.4</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>I'mtrying to usepointers tomanipulate an array of <TT>int</TT>s.What's wrong with this code?<pre> int array[5], i, *ip; for(i = 0; i < 5; i++) array[i] = i; ip = array; printf("%d\n", *(ip + 3 * sizeof(int)));</pre>I expected the last line to print 3,but it printed garbage.</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>You're doing a bit more work than you have to,or should.Pointer arithmetic in C is always automatically scaledby the size of the objects pointed to.What you want to say is simply<pre> printf("%d\n", *(ip + 3)); /* or ip[3] -- see Q <a href="../aryptr/aryptrequiv.html">6.3</a> */</pre>which will print the third element of the array.In code like this,you don't need to worryabout scaling by the size of the pointed-toelements--byattempting to doso explicitly,you inadvertently tried to accessa nonexistent elementpast the end of the array(probably <TT>array[6]</TT> or <TT>array[12]</TT>,depending on <TT>sizeof(int)</TT> on your machine).</p><p>See, however, question <a href="../malloc/noscale.html">7.19b</a>.</p><p>References:K&R1 Sec. 5.3 p. 94<br>K&R2 Sec. 5.4 p. 103<br>ISO Sec. 6.3.6<br>H&S Sec. 7.6.2 p. 204<br></p><!-- aend --><p><hr><a href="unopprec2.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="castincr.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/ptrs/explscale.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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