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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!-- but may not be published or retransmitted without explicit permission.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/accessloc0.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 5.19</title><link href="runtime0.html" rev=precedes><link href="nullpassign.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="runtime0.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="nullpassign.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 5.19</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>How can I accessan interrupt vectorlocated atthe machine's location 0?If I set a pointer to <TT>0</TT>,the compiler might translate it to some nonzero internal nullpointer value.</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>Since whatever is at location 0 isobviouslymachine dependent,you're free to use whatever machine-dependent trick will work toget there.Read your vendor's documentation(and seesection<a href="../osdep/index.html">19</a>).It's likely thatif it's at all meaningfulfor you to beaccessinglocation 0,the system will be set up to make it reasonably easy to do so.Some possibilities are:<OL><li>Simply set a pointer to <TT>0</TT>.(This is the way that doesn't have to work,but if it's meaningful,it probably will.)<li>Assign the integer <TT>0</TT> to an <TT>int</TT> variable,and convert that <TT>int</TT> to a pointer.(This is also not guaranteed to work,but it probably will.)<li>Use a unionto set the bits of a pointer variable to 0:<pre> union { int *u_p; int u_i; /* assumes sizeof(int) >= sizeof(int *) */ } p; p.u_i = 0;</pre><li>Use <TT>memset</TT>to set the bits of a pointer variable to 0:<pre> memset((void *)&p, 0, sizeof(p));</pre><li>Declare an external variable or array<pre> extern int location0;</pre>and use an assembly language file,or some special linker invocation,to arrange that this symbolrefers to(i.e. the variableis placed at)address 0.</OL></p><p>See also questions<a href="../ptrs/int2ptr.html">4.14</a>and<a href="../osdep/rawmemadr.html">19.25</a>.</p><p>References:K&R1 Sec. A14.4 p. 210<br>K&R2 Sec. A6.6 p. 199<br>ISO Sec. 6.3.4<br>Rationale Sec. 3.3.4<br>H&S Sec. 6.2.7 pp. 171-2<br></p><!-- aend --><p><hr><a href="runtime0.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="nullpassign.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/accessloc0.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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