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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!-- but may not be published or retransmitted without explicit permission.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/popen.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 19.30</title><link href="systemret.html" rev=precedes><link href="exepath.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="systemret.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="exepath.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 19.30</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>How can I invokeanother programor commandandtrapits output?</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>Unixand some other systems provide a <TT>popen</TT>function,which sets upa stdio streamon a pipeconnected to the processrunning a command,so that thecalling program can read the output(oralternativelysupply the input).Using <TT>popen</TT>,the last example fromquestion <a href="system2.html">19.28</a>would look like<pre> extern FILE *popen(); sprintf(cmdbuf, "sort < %s", datafile); fp = popen(cmdbuf, "r"); /* ...now read sorted data from fp... */ pclose(fp);</pre>(Do be sureto call <TT>pclose</TT>,as shown;leaving it out will seem to work at firstbut may eventually run you out of processesorfile descriptors.)</p><p>If you can't use <TT>popen</TT>,you may be able to use <TT>system</TT>,with the output going to a filewhich you then open and read,as the code in question <a href="system2.html">19.28</a> was doing already.<a href="concur.html" rel=subdocument>[footnote]</a></p><p>If you're using Unix and <TT>popen</TT> isn't sufficient,you can learn about<TT>pipe</TT>,<TT>dup</TT>, <TT>fork</TT>,and<TT>exec</TT>.</p><p>(One thing thatprobably would <em>not</em> work,by the way,would beto use <TT>freopen</TT>.)</p><p>References:PCS Sec. 11 p. 169<br></p><!-- aend --><p><hr><a href="systemret.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="exepath.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/popen.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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