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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!-- but may not be published or retransmitted without explicit permission.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 null.sgml dated Wed Dec 21 13:03:25 2005 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/null/confused2.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:48 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 5.15</title><link href="confusion.html" rev=precedes><link href="confusion4.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="confusion.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="confusion4.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 5.15</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>I'm confused.I just can't understand all this null pointer stuff.</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>Here aretwo simple rulesyou can follow:<OL><li>When you wanta null pointer constant in source code,use ``<TT>0</TT>'' or ``<TT>NULL</TT>''.<li>If the usage of ``<TT>0</TT>'' or ``<TT>NULL</TT>'' isan argumentin a function call,castit to the pointer type expected by the function being called.</OL></p><p>The rest ofthe discussionhas to do with other people's misunderstandings,with the internal representation of null pointers(which you shouldn't need to know),andwith the complexities of function prototypes.(Taking those complexities into account,we find that rule 2 is conservative<a href="ptrargcast.html" rel=subdocument>[footnote]</a>,of course;but it doesn't hurt.)Understand questions<a href="null1.html">5.1</a>,<a href="null2.html">5.2</a>,and<a href="macro.html">5.4</a>,and consider<a href="ptrtest.html">5.3</a>,<a href="nullor0.html">5.9</a>,<a href="varieties.html">5.13</a>,and<a href="confusion.html">5.14</a>,and you'll do fine.</p><!-- aend --><p><hr><a href="confusion.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="confusion4.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/null/confused2.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:48 GMT --></html>⌨️ 快捷键说明
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