getopt.c

Many C samples. It is a good sample for students to learn C language.

/*  File   : getopt.c
    Author : Henry Spencer, University of Toronto
    Updated: 28 April 1984
    Purpose: get option letter from argv.
*/

#include <stdio.h>
#include "strings.h"

char	*optarg;	/* Global argument pointer. */
int	optind = 0;	/* Global argv index. */

int getopt(argc, argv, optstring)
    int argc;
    char *argv[];
    char *optstring;
    {
	register int c;
	register char *place;
	static char *scan = NullS;	/* Private scan pointer. */

	optarg = NullS;

	if (scan == NullS || *scan == '\0') {
	    if (optind == 0) optind++;
	    if (optind >= argc) return EOF;
	    place = argv[optind];
	    if (place[0] != '-' || place[1] == '\0') return EOF;
	    optind++;
	    if (place[1] == '-' && place[2] == '\0') return EOF;
	    scan = place+1;
	}

	c = *scan++;
	place = index(optstring, c);
	if (place == NullS || c == ':') {
	    fprintf(stderr, "%s: unknown option %c\n", argv[0], c);
	    return '?';
	}
	if (*++place == ':') {
	    if (*scan != '\0') {
		optarg = scan, scan = NullS;
	    } else {
		optarg = argv[optind], optind++;
	    }
	}
	return c;
    }