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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!-- but may not be published or retransmitted without explicit permission.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 lib1.sgml dated Sat Feb 7 18:46:53 2004 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/lib/strncpy.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:58 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 13.2</title><link href="itoa.html" rev=precedes><link href="substr.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="itoa.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="substr.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 13.2</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>Why does <TT>strncpy</TT> not alwaysplace a <TT>'\0'</TT> terminatorin the destination string?</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font><TT>strncpy</TT>was first designed to handle a now-obsolete data structure,the fixed-length, not-necessarily-<TT>\0</TT>-terminated``string.''<a href="strncpyexamp.html" rel=subdocument>[footnote]</a><TT>strncpy</TT> is admittedly a bit cumbersome to use in other contexts,since you must often append a<TT>'\0'</TT> to the destinationstring by hand.</p><p>You can get around the problem by using <TT>strncat</TT>instead of <TT>strncpy</TT>.Ifthe destination string starts out empty(that is, if you do<TT>*dest = '\0'</TT>first),<TT>strncat</TT> does what you probably wanted <TT>strncpy</TT> to do:<pre> *dest = '\0'; strncat(dest, source, n);</pre>This code copies up to <TT>n</TT> characters,and always appends a <TT>\0</TT>.</p><p>Another possibility is<pre><TT>sprintf(dest, "%.*s", n, source)</TT></pre>(though,strictly speaking,this is only guaranteed to work for <TT>n</TT> <= 509).</p><p>Whenarbitrarybytes(as opposed to strings)are being copied,<TT>memcpy</TT> is usually a more appropriate function to usethan <TT>strncpy</TT>.</p><!-- aend --><p><hr><a href="itoa.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="substr.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/lib/strncpy.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:58 GMT --></html>⌨️ 快捷键说明
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