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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!-- but may not be published or retransmitted without explicit permission.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/enumvsdefine.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:46 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 2.22</title><link href="taggedunion.html" rev=precedes><link href="enumport.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="taggedunion.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="enumport.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 2.22</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>What's the difference betweenan enumeration and a set ofpreprocessor <TT>#define</TT>s?</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>There islittledifference.TheC Standardsays that enumerationshave integral typeand that enumeration constants are of type <TT>int</TT>,so bothmay be freely intermixed withotherintegraltypes, without errors.(If,on the other hand,such intermixing were disallowed without explicit casts,judicious use of enumerations could catch certain programming errors.)</p><p>Someadvantages of enumerations arethat the numericvalues are automatically assigned,that a debugger may be able to displaythe symbolic values when enumeration variables are examined,andthat they obey block scope.(Acompiler mayalsogenerate nonfatal warnings when enumerationsareindiscriminately mixed,since doing socan still be considered bad styleeven thoughit is not strictly illegal.)A disadvantageis that the programmer has little controlover those nonfatal warnings;some programmers also resent not having controlover the sizes of enumeration variables.</p><p>References:K&R2 Sec. 2.3 p. 39, Sec. A4.2 p. 196<br>ISO Sec. 6.1.2.5, Sec. 6.5.2, Sec. 6.5.2.2, Annex F<br>H&S Sec. 5.5 pp. 127-9, Sec. 5.11.2 p. 153<br></p><!-- aend --><p><hr><a href="taggedunion.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="enumport.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/enumvsdefine.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:46 GMT --></html>⌨️ 快捷键说明
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