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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!-- but may not be published or retransmitted without explicit permission.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 21:47:46 2005 by faqproc version 2.7 --><!-- from source file bool.sgml dated Thu Jul 15 19:41:07 2004 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/bool/booltype.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:53 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 9.1</title><link href="../charstring/wchar.html" rev=precedes><link href="bool2.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="../charstring/wchar.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="bool2.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 9.1</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>What is the right type to use for Boolean values in C?Is there a standard type?ShouldI use<TT>#define</TT>s or enumsfor the true and false values?</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>Traditionally,C did not provide a standard Boolean type,partlyand partly to allow the programmer to make the appropriatespace/time tradeoff.(Using an <TT>int</TT>may be faster,while using <TT>char</TT>maysave data space.<a href="bitfield.html" rel=subdocument>[footnote]</a>Smaller types may make thegeneratedcode bigger or slower,though,if they require lots of conversions to and from <TT>int</TT>.)</p><p>However, C99 <em>does</em> define a standard Boolean type,as long as you include <TT><stdbool.h></TT>.</p><p>If you decide to define them yourself,the choice between <TT>#define</TT>sand enumeration constantsfor the true/false valuesis arbitrary and notterribly interesting(see also questions<a href="../struct/enumvsdefine.html">2.22</a>and<a href="../style/stylewars.html">17.10</a>).Use any of<br><br><TT><pre> #define TRUE 1 #define YES 1 #define FALSE 0 #define NO 0 enum bool {false, true}; enum bool {no, yes};</pre></TT><br><br>or use raw 1 and 0,as long as you are consistent within one program or project.(An enumeration may be preferable if your debuggershows the names of enumeration constantswhen examining variables.)</p><p>You may also want to use a <TT>typedef</TT>:<pre> typedef int bool;or typedef char bool;or typedef enum {false, true} bool;</pre></p><p>Some people prefer variants like<pre> #define TRUE (1==1) #define FALSE (!TRUE)</pre>or define ``helper'' macros such as<pre> #define Istrue(e) ((e) != 0)</pre>These don't buy anything (see question<a href="bool2.html">9.2</a>;see also questions<a href="../null/nullptrmacro.html">5.12</a>and<a href="../cpp/slm.html">10.2</a>).</p><!-- aend --><p><hr><a href="../charstring/wchar.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="bool2.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/bool/booltype.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:53 GMT --></html>⌨️ 快捷键说明
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