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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!-- but may not be published or retransmitted without explicit permission.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 misctechn.sgml dated Sat Sep 28 22:23:36 2002 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/misc/argv.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:59:04 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 20.3</title><link href="ragged.html" rev=precedes><link href="errno.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="ragged.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="errno.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 20.3</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>How can I open files mentioned on the command line,and parse option flags?</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>Here is a skeleton which implements a traditional Unix-style<TT>argv</TT> parse,handling option flags beginning with <TT>-</TT>,and optional filenames.(The two flags acceptedby this exampleare <TT>-a</TT> and <TT>-b</TT>;<TT>-b</TT> takes an argument.)<pre>#include <stdio.h>#include <string.h>#include <errno.h>main(int argc, char *argv[]){ int argi; int aflag = 0; char *bval = NULL; for(argi = 1; argi < argc && argv[argi][0] == '-'; argi++) { char *p; for(p = &argv[argi][1]; *p != '\0'; p++) { switch(*p) { case 'a': aflag = 1; printf("-a seen\n"); break; case 'b': bval = argv[++argi]; printf("-b seen (\"%s\")\n", bval); break; default: fprintf(stderr, "unknown option -%c\n", *p); } } } if(argi >= argc) { /* no filename arguments; process stdin */ printf("processing standard input\n"); } else { /* process filename arguments */ for(; argi < argc; argi++) { FILE *ifp = fopen(argv[argi], "r"); if(ifp == NULL) { fprintf(stderr, "can't open %s: %s\n", argv[argi], strerror(errno)); continue; } printf("processing %s\n", argv[argi]); fclose(ifp); } } return 0;}</pre>(This code assumes that <TT>fopen</TT>sets <TT>errno</TT> when it fails,which is not guaranteed,but usually works,and makes error messages much more useful.See also question <a href="errno.html">20.4</a>.)</p><p>There are several canned functions availablefor doing command line parsing in a standard way;the most popular one is<TT>getopt</TT>(see also question <a href="../resources/sources.html">18.16</a>).Here is the above example,rewritten to use <TT>getopt</TT>:<pre>extern char *optarg;extern int optind;main(int argc, char *argv[]){ int aflag = 0; char *bval = NULL; int c; while((c = getopt(argc, argv, "ab:")) != -1) switch(c) { case 'a': aflag = 1; printf("-a seen\n"); break; case 'b': bval = optarg; printf("-b seen (\"%s\")\n", bval); break; } if(optind >= argc) { /* no filename arguments; process stdin */ printf("processing standard input\n"); } else { /* process filename arguments */ for(; optind < argc; optind++) { FILE *ifp = fopen(argv[optind], "r"); if(ifp == NULL) { fprintf(stderr, "can't open %s: %s\n", argv[optind], strerror(errno)); continue; } printf("processing %s\n", argv[optind]); fclose(ifp); } } return 0;}</pre></p><p>The examples above overlook a number of nuances:a lone``<TT>-</TT>'' is often taken to mean``read standard input'';the marker ``<TT>--</TT>'' often signifies the end of the options(proper versions of <TT>getopt</TT> do handle this);it's traditional to print a usage messagewhen a command is invoked with improper or missing arguments.</p><p>If you're wondering how <TT>argv</TT> is laid out in memory,it's actually a``ragged array'';see the picture inquestion <a href="ragged.html">20.2</a>.See also questions<a href="../charstring/stringeq.html">8.2</a>,<a href="../lib/regex.html">13.7</a>,and<a href="../osdep/readdir.html">19.20</a>.</p><p>References:K&R1 Sec. 5.11 pp. 110-114<br>K&R2 Sec. 5.10 pp. 114-118<br>ISO Sec. 5.1.2.2.1<br>H&S Sec. 20.1 p. 416<br>PCS Sec. 5.6 pp. 81-2, Sec. 11 p. 159, pp. 339-40 Appendix F<br>Schumacher, ed.,<I>Software Solutions in C</I> Sec. 4 pp. 75-85<br></p><!-- aend --><p><hr><a href="ragged.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="errno.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/misc/argv.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:59:04 GMT --></html>⌨️ 快捷键说明
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