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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><HTML><HEAD> <META NAME="GENERATOR" CONTENT="LinuxDoc-Tools 0.9.21"> <TITLE>libapr(apache portable runtime) programming tutorial: command line options</TITLE> <LINK HREF="apr-tutorial-11.html" REL=next> <LINK HREF="apr-tutorial-9.html" REL=previous> <LINK HREF="apr-tutorial.html#toc10" REL=contents></HEAD><BODY><A HREF="apr-tutorial-11.html">Next</A><A HREF="apr-tutorial-9.html">Previous</A><A HREF="apr-tutorial.html#toc10">Contents</A><HR><H2><A NAME="s10">10.</A> <A HREF="apr-tutorial.html#toc10">command line options</A></H2><P>For CLI(command line interface) tools, command line options are popular. libapr provides APIs to handle command line options easily. Here is an excerpted code from <A HREF="../sample/getopt-sample.c">getopt-sample.c</A>.</P><P>/* excerpted from <A HREF="../sample/getopt-sample.c">getopt-sample.c</A> */<BLOCKQUOTE><CODE><PRE>static const apr_getopt_option_t opt_option[] = { /* long-option, short-option, has-arg flag, description */ { "in", 'i', TRUE, "input file" }, /* -i name or --in name */ { "out", 'o', TRUE, "output file" }, /* -o name or --out name */ { "help", 'h', FALSE, "show help" }, /* -h or --help */ { NULL, 0, 0, NULL }, /* end (a.k.a. sentinel) */};</PRE></CODE></BLOCKQUOTE></P><P>At first, we should supply an array of apr_getopt_option_t elements. We call it option-list. Each element has four variables, i.e. long option, short option, flag of the trailing argument, and description. A long option is specified as '--help'. A short option is specified as '-h'. Short options are mandatory and long options are optional. We can set a long option to NULL. The third variable is flag of the existence of trailing argument. If a command line option works as '--in filename', i.e. the trailing argument is required, we have to set the flag to TRUE. If you run the program without the required argument, e.g. './a.out -in', it causes an error.The option-list must have a sentinel element as described above.</P><P>To parse actual command line options based on the option-list, we have to call apr_getopt_init() at first. That initializes apr_getopt_t object. Next, we keep calling apr_getopt_long() while it returns APR_SUCCESS. Here is an excerpted code from <A HREF="../sample/getopt-sample.c">getopt-sample.c</A>.</P><P>/* excerpted from <A HREF="../sample/getopt-sample.c">getopt-sample.c</A> */<BLOCKQUOTE><CODE><PRE>/* initialize apr_getopt_t */apr_getopt_t *opt;apr_getopt_init(&opt, mp, argc, argv);/* parse the all options based on opt_option[] */while ((rv = apr_getopt_long(opt, opt_option, &optch, &optarg)) == APR_SUCCESS) { switch (optch) { case 'i': ...OMIT</PRE></CODE></BLOCKQUOTE></P><P>During the loop, apr_getopt_long() processes the actual command line option one by one. If the option found is in the option-list, apr_getopt_long() returns APR_SUCCESS and set optch's value. When the option has the trailing argument, apr_getopt_long() parses it and set optarg's value. </P><P>I show you an example. Let's think about the case that you run the program as './getopt-sample -h -i foo.txt'. At the first loop, apr_getopt_long() finds 'h' in the option-list. Then, apr_getopt_long() returns APR_SUCCESS and set optch to 'h'. At the next loop, apr_getopt_long() finds 'i' in the option-list and 'i' requiring the trailing argument, so it parses the trailing argument, 'foo.txt'. Thus, apr_getopt_long() returns APR_SUCCESS, and set optch to 'i' and optarg to "foo.txt". At the next loop, apr_getopt_long() finds no more options, so returns APR_EOF.</P><HR><A HREF="apr-tutorial-11.html">Next</A><A HREF="apr-tutorial-9.html">Previous</A><A HREF="apr-tutorial.html#toc10">Contents</A></BODY></HTML>?? 快捷鍵說明
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