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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!-- but may not be published or retransmitted without explicit permission.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 stdio.sgml dated Wed Dec 21 13:07:57 2005 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/stdio/fupdate.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 12.30</title><link href="fopenpath.html" rev=precedes><link href="insdelrec.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="fopenpath.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="insdelrec.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 12.30</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>I'm trying to update a file in place,by using <TT>fopen</TT> mode <TT>"r+"</TT>,reading a certain string,and writing back a modified string,but it's not working.</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>Be sure to call <TT>fseek</TT>before you write,bothto seek backto the beginning of the string you're trying to overwrite,andbecausean <TT>fseek</TT> or <TT>fflush</TT>is always required betweenreading and writing in the read/write <TT>"+"</TT> modes.Also, remember that you can only overwrite characterswith the same number of replacementcharacters;there is no way to insert or delete characters in place.Finally,rememberthat overwriting in text modemay truncate the file at that point,and that you may have to preserve line lengths.See also question<a href="../osdep/insdelrec.html">19.14</a>.</p><p>References:ISO Sec. 7.9.5.3<br></p><!-- aend --><p><hr><a href="fopenpath.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="insdelrec.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/stdio/fupdate.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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