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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!-- but may not be published or retransmitted without explicit permission.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 struct.sgml dated Wed Dec 21 16:15:32 2005 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/struct/typedef.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:45 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 2.1</title><link href="../decl/initunion.html" rev=precedes><link href="impltypedef.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="../decl/initunion.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="impltypedef.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 2.1</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>What's the difference betweenthese two declarations?<pre> struct x1 { ... }; typedef struct { ... } x2;</pre></p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>The first form declares a <a href="../sx1/index.html#structure tag"><dfn>structure tag</dfn></a>;the second declares a <a href="../sx1/index.html#typedef"><dfn>typedef</dfn></a>.Themaindifference isthatthe second declaration is of a slightly more abstracttype--itsusers don't necessarily know that it is a structure,andthe keyword <TT>struct</TT> is not used when declaring instances ofit:<pre> x2 b;</pre></p><p>Structures declared withtags,on the other hand,must be defined with the<pre> struct x1 a;</pre>form.<a href="cplpl.html" rel=subdocument>[footnote]</a></p><p>(It'salso possible to play it both ways:<pre> typedef struct x3 { ... } x3;</pre>It's legal,if potentially obscure,to use the same name for both the tag and the typedef,since they live in separate namespaces.See question <a href="../decl/namespace.html">1.29</a>.)</p><!-- aend --><p><hr><a href="../decl/initunion.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="impltypedef.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/struct/typedef.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:45 GMT --></html>⌨️ 快捷键说明
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