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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!-- but may not be published or retransmitted without explicit permission.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 21:47:47 2005 by faqproc version 2.7 --><!-- from source file osdepproc.sgml dated Sat Feb 7 19:18:20 2004 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/osdep/system2.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:59:03 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 19.28</title><link href="system.html" rev=precedes><link href="systemret.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="system.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="systemret.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 19.28</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>How can I call <TT>system</TT> when parameters(filenames, etc.)of the executed commandaren't known until run time?</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>Just use <TT>sprintf</TT>(or perhaps <TT>strcpy</TT> and <TT>strcat</TT>)to build the command string in abuffer,then call <TT>system</TT> with that buffer.(Make sure the buffer is allocated with enough space;see also questions <a href="../malloc/malloc2.html">7.2</a> and <a href="../stdio/sprintfsize.html">12.21</a>.)</p><p>Here isa contrived examplesuggesting how you mightbuild a data file,then sort it(assuming the existence of a sort utility,and Unix-or MS-DOS-styleinput/output redirection):<pre> char *datafile = "file.dat"; char *sortedfile = "file.sort"; char cmdbuf[50]; FILE *fp = fopen(datafile, "w"); /* ...write to fp to build data file... */ fclose(fp); sprintf(cmdbuf, "sort < %s > %s", datafile, sortedfile); system(cmdbuf); fp = fopen(sortedfile, "r"); /* ...now read sorted data from fp... */</pre></p><p>See also question <a href="../stdio/constrpath.html">12.28b</a>.</p><!-- aend --><p><hr><a href="system.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="systemret.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/osdep/system2.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:59:03 GMT --></html>⌨️ 快捷键说明
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