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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!-- but may not be published or retransmitted without explicit permission.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 decl.sgml dated Wed Dec 21 12:56:18 2005 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/decl/selfrefstruct.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:44 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 1.14</title><link href="typedefvsdefine.html" rev=precedes><link href="mutrefstructs.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="typedefvsdefine.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="mutrefstructs.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 1.14</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>I can't seem to define a linked listsuccessfully.I tried<pre> typedef struct { char *item; NODEPTR next; } *NODEPTR;</pre>but the compiler gave me error messages.Can't a structure in C contain a pointer to itself?</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>Structures in C can certainly contain pointers to themselves; thediscussion and example in section 6.5 of K&Rmake this clear.</p><p>The problem withthis example isthe typedef.A typedef defines a new name for a type,and in simpler cases<a href="immtypedef.html" rel=subdocument>[footnote]</a>you can define a new structure typeand a typedef for itat the same time,but not in this case.A typedef declaration cannot be used until it is defined,and in the fragment above,it is not yetdefinedat the point wherethe <TT>next</TT> field is declared.</p><p>To fixthis code,firstgive the structure a tag (e.g. ``<TT>struct node</TT>'').Then,declare the <TT>next</TT> fieldasa simple<TT>struct node *</TT>,or disentangle the typedef declaration from the structure definition,or both.Onecorrectedversion would be:<pre> typedef struct node { char *item; struct node *next; } *NODEPTR;</pre>You could also precede the struct declarationwiththe typedef,in which case you could use the <TT>NODEPTR</TT> typedef when declaringthe <TT>next</TT> field,after all:<pre> typedef struct node *NODEPTR; struct node { char *item; NODEPTR next; };</pre>(In this case,you declare a new tyedef name involving <TT>struct node</TT>even though <TT>struct node</TT>has not beencompletelydefinedyet;this you're allowed to do.<a href="jst1.html" rel=subdocument>[footnote]</a>)</p><p>Finally,here is a rearrangement incorporating both suggestions:<pre> struct node { char *item; struct node *next; }; typedef struct node *NODEPTR;</pre></p><p>(It's a matter of style which method to prefer;seesection<a href="../style/index.html">17</a>.)</p><p>See also questions<a href="mutrefstructs.html">1.15</a>and<a href="../struct/typedef.html">2.1</a>.</p><p>References:K&R1 Sec. 6.5 p. 101<br>K&R2 Sec. 6.5 p. 139<br>ISO Sec. 6.5.2, Sec. 6.5.2.3<br>H&S Sec. 5.6.1 pp. 132-3<br></p><!-- aend --><p><hr><a href="typedefvsdefine.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="mutrefstructs.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/decl/selfrefstruct.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:44 GMT --></html>⌨️ 快捷键说明
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