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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!-- but may not be published or retransmitted without explicit permission.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 cpp.sgml dated Wed Dec 21 13:52:14 2005 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/cpp/nestincl.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:54 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 10.7</title><link href="hfiles.html" rev=precedes><link href="inclkinds.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="hfiles.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="inclkinds.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 10.7</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>Is it acceptable for one header file to <TT>#include</TT> another?</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>It's a question of style,and thus receives considerable debate.Many people believe that``nested <TT>#include</TT> files''are to be avoided:the prestigious Indian Hill Style Guide(see question<a href="../style/guides.html">17.9</a>)disparages them;they can make it harder to find relevant definitions;they can lead to multiple-definition errors if a file is <TT>#include</TT>d twice;they can lead toincreased compilation time;andthey make manual Makefile maintenance very difficult.On the other hand,they make it possible to use header files in a modular way (aheader file can <TT>#include</TT> what it needs itself,rather thanrequiring each <TT>#include</TT>r to do so);a tool like <TT>grep</TT>(or a tags file)makes it easy to find definitions no matter where they are;a popular trickalong the lines of:<pre> #ifndef HFILENAME_USED #define HFILENAME_USED ...header file contents... #endif</pre>(where a differentbracketingmacro nameis used for each header file)makes a header file ``idempotent''so that it can safely be <TT>#include</TT>d multiple times;a clever compiler can avoid expending any more timeon later instances ofan already-included header;and automated Makefile maintenance tools(which are a virtual necessity in large projects anyway;see question <a href="../resources/tools.html">18.1</a>)handle dependency generation in the face of nested <TT>#include</TT> files easily.See also question <a href="../style/stylewars.html">17.10</a>.</p><p>References:Rationale Sec. 4.1.2<br></p><!-- aend --><p><hr><a href="hfiles.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="inclkinds.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/cpp/nestincl.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:54 GMT --></html>⌨️ 快捷键说明
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