📄 lazyalloc.html
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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!-- but may not be published or retransmitted without explicit permission.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 malloc.sgml dated Wed Dec 21 13:50:44 2005 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/malloc/lazyalloc.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:50 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 7.14</title><link href="malloc0xref.html" rev=precedes><link href="sizetlong.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="malloc0xref.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="sizetlong.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 7.14</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>I've heard that some operating systemsdon't actually allocate <TT>malloc</TT>'ed memoryuntiltheprogram tries touseit.Is this legal?</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>It's hard to say.The Standard doesn't say that systems can act this way,but it doesn'texplicitlysay that they can't, either.(Such a ``deferred failure'' implementationwould not seem to conform to the implied requirements of the Standard.)</p><p>Theconspicuousproblem is that,by the timethe program gets around to trying to use the memory,there might not be any.Theprogramin this case must typically be killed by the operating system,since the semantics of C provide no recourse.(Obviously,<TT>malloc</TT> is supposed to return a null pointerif there's no memory,so that the program--aslong as it checks <TT>malloc</TT>'s return value at all--nevertries to use more memory than is available.)</p><p>Systems thatdo this ``lazy allocation''usually provide extra signalsindicating that memory is dangerously low,but portable or naïve programs won't catch them.Some systems that do lazy allocationalso provide a way to turn it off(reverting to traditional <TT>malloc</TT> semantics),on a per-process or per-user basis,but the details vary from system to system.</p><p>Additional links:A<a href="lazyalloc2.html">longer explanation</a>of the tradeoffs concerning ``lazy allocation''</p><p>References:ISO Sec. 7.10.3<br></p><!-- aend --><p><hr><a href="malloc0xref.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="sizetlong.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/malloc/lazyalloc.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:51 GMT --></html>⌨️ 快捷键说明
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