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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!-- but may not be published or retransmitted without explicit permission.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/int2ptr.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:48 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 4.14</title><link href="generic.html" rev=precedes><link href="int2charp.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="generic.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="int2charp.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 4.14</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>How are integers converted to and from pointers?Can I temporarily stuff an integer into a pointer,or vice versa?</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>Once upon a time,it was guaranteed that a pointer could be converted to an integer(though one never knewwhether an <TT>int</TT> or a <TT>long</TT> might be required),and that an integer could be converted to a pointer,and that a pointer remained unchanged when converted to a (large enough)integer and back again,andthat the conversions(and anymapping)were intended to be``unsurprising to those who know the addressing structure of the machine.''In other words,there issomeprecedent andsupport forinteger/pointerconversions,buttheyhave always been machine dependent,and hence nonportable.Explicit casts have always been required(though early compilers rarely complained if you left them out).</p><p>The ANSI/ISO C Standard,in order to ensure that C is widely implementable,hasweakenedthose earlier guarantees.Pointer-to-integer and integer-to-pointer conversionsare implementation-defined(see question <a href="../ansi/undef.html">11.33</a>),andthereis no longer any guarantee that pointers can be converted to integers and back, without change.</p><p>Forcingpointers into integers,or integers into pointers,has never been good practice.When you need a generic slot that can hold eitherkind of data,a union is a much betteridea.</p><p>See also questions<a href="int2charp.html">4.15</a>,<a href="../null/runtime0.html">5.18</a>,and <a href="../osdep/rawmemadr.html">19.25</a>.</p><p>References:K&R1 Sec. A14.4 p. 210<br>K&R2 Sec. A6.6 p. 199<br>ISO Sec. 6.3.4<br>Rationale Sec. 3.3.4<br>H&S Sec. 6.2.3 p. 170, Sec. 6.2.7 pp. 171-2<br></p><!-- aend --><p><hr><a href="generic.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="int2charp.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/int2ptr.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:48 GMT --></html>⌨️ 快捷键说明
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