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copied!<p>Use <a href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/getopt.html" rel="noreferrer"><code>getopt()</code></a>, or perhaps <a href="http://www.gnu.org/software/libc/manual/html_node/Getopt-Long-Options.html" rel="noreferrer"><code>getopt_long()</code></a>.</p> <pre><code>int iflag = 0; enum { WORD_MODE, LINE_MODE } op_mode = WORD_MODE; // Default set int opt; while ((opt = getopt(argc, argv, "ilw") != -1) { switch (opt) { case 'i': iflag = 1; break; case 'l': op_mode = LINE_MODE; break; case 'w': op_mode = WORD_MODE; break; default: fprintf(stderr, "Usage: %s [-ilw] [file ...]\n", argv[0]); exit(EXIT_FAILURE); } } /* Process file names or stdin */ if (optind >= argc) process(stdin, "(standard input)", op_mode); else { int i; for (i = optind; i < argc; i++) { FILE *fp = fopen(argv[i], "r"); if (fp == 0) fprintf(stderr, "%s: failed to open %s (%d %s)\n", argv[0], argv[i], errno, strerror(errno)); else { process(fp, argv[i], op_mode); fclose(fp); } } } </code></pre> <p>Note that you need to determine which headers to include (I make it 4 that are required), and the way I wrote the <code>op_mode</code> type means you have a problem in the function <code>process()</code> - you can't access the enumeration down there. It's best to move the enumeration outside the function; you might even make <code>op_mode</code> a file-scope variable without external linkage (a fancy way of saying <code>static</code>) to avoid passing it to the function. This code does not handle <code>-</code> as a synonym for standard input, another exercise for the reader. Note that <code>getopt()</code> automatically takes care of <code>--</code> to mark the end of options for you.</p> <p>I've not run any version of the typing above past a compiler; there could be mistakes in it.</p> <hr> <p>For extra credit, write a (library) function:</p> <pre><code>int filter(int argc, char **argv, int idx, int (*function)(FILE *fp, const char *fn)); </code></pre> <p>which encapsulates the logic for processing file name options after the <code>getopt()</code> loop. It should handle <code>-</code> as standard input. Note that using this would indicate that <code>op_mode</code> should be a static file scope variable. The <code>filter()</code> function takes <code>argc</code>, <code>argv</code>, <code>optind</code> and a pointer to the processing function. It should return 0 (EXIT_SUCCESS) if it was able to open all the files and all invocations of the function reported 0, otherwise 1 (or EXIT_FAILURE). Having such a function simplifies writing Unix-style 'filter' programs that read files specified on the command line or standard input.</p>

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