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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!-- but may not be published or retransmitted without explicit permission.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 malloc.sgml dated Wed Dec 21 13:50:44 2005 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/malloc/sizetlong.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:51 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 7.15</title><link href="lazyalloc.html" rev=precedes><link href="sizewrap.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="lazyalloc.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="sizewrap.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 7.15</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font><TT>malloc</TT>isreturning crazy pointer values,but I <em>did</em> read question <a href="decl.html">7.6</a>and I have included the line<pre> extern void *malloc();</pre>before I call it.</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font><TT>malloc</TT> accepts an argument of type <TT>size_t</TT>,and <TT>size_t</TT> may bedefinedas<TT>unsigned long</TT>.If you are passing <TT>int</TT>s(or even <TT>unsigned int</TT>s),<TT>malloc</TT> may be receiving garbage(orsimilarlyif you are passing a <TT>long</TT> but <TT>size_t</TT> is<TT>int</TT>).</p><p>In general,it is much, much saferto declare standard library functionsby #including the appropriate header files,rather than typing <TT>extern</TT> declarations yourself.See also question <a href="sizewrap.html">7.16</a>.</p><p>(A related problem is that it is not safe to print <TT>size_t</TT> values,including the result of <TT>sizeof</TT>,using <TT>printf</TT>'s <TT>%d</TT> format.The portable approachis to use an explicit <TT>(unsigned long)</TT> cast,and <TT>%lu</TT> format:<TT>printf("%lu\n", (unsigned long)sizeof(int))</TT>.See also question <a href="../varargs/proto2.html">15.3</a>.)</p><p>References:ISO Sec. 7.1.6, Sec. 7.1.7<br></p><!-- aend --><p><hr><a href="lazyalloc.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="sizewrap.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/sizetlong.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:51 GMT --></html>⌨️ 快捷键说明
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