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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!-- but may not be published or retransmitted without explicit permission.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/castincr.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 4.5</title><link href="explscale.html" rev=precedes><link href="voidparith.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="explscale.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="voidparith.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 4.5</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>Ihavea <TT>char *</TT> pointerthat happens to point tosome <TT>int</TT>s,and I want to step it over them.Why doesn't<pre>((int *)p)++;</pre>work?</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>In C, a cast operatordoes not mean``pretend these bits have a different type,and treat them accordingly'';itis a conversion operator,and by definition it yields an rvalue,which cannot be assigned to,or incremented with <TT>++</TT>.(It iseither an accidentor a deliberate but nonstandard extensionif a particular compiler acceptsexpressions such as the above.)Say what you mean:use<pre> p = (char *)((int *)p + 1);</pre>or(since <TT>p</TT> is a <TT>char *</TT>)simply<pre> p += sizeof(int);</pre>or(to be really explicit)<pre> int *ip = (int *)p; p = (char *)(ip + 1);</pre></p><p>Whenpossible,however,you should choose appropriatepointertypesin the first place,rather thantrying to treat one type as another.</p><p>See also question <a href="../strangeprob/ptralign.html">16.7</a>.</p><p>References:K&R2 Sec. A7.5 p. 205<br>ISO Sec. 6.3.4<br>Rationale Sec. 3.3.2.4<br>H&S Sec. 7.1 pp. 179-80<br></p><!-- aend --><p><hr><a href="explscale.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="voidparith.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/castincr.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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