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getopt.c
/*****************************************************************************
 *
 *  MODULE NAME : GETOPT.C
 *
 *  COPYRIGHTS:
 *             This module contains code made available by IBM
 *             Corporation on an AS IS basis.  Any one receiving the
 *             module is considered to be licensed under IBM copyrights
 *             to use the IBM-provided source code in any way he or she
 *             deems fit, including copying it, compiling it, modifying
 *             it, and redistributing it, with or without
 *             modifications.  No license under any IBM patents or
 *             patent applications is to be implied from this copyright
 *             license.
 *
 *             A user of the module should understand that IBM cannot
 *             provide technical support for the module and will not be
 *             responsible for any consequences of use of the program.
 *
 *             Any notices, including this one, are not to be removed
 *             from the module without the prior written consent of
 *             IBM.
 *
 *  AUTHOR:   Original author:
 *                 G. R. Blair (BOBBLAIR at AUSVM1)
 *                 Internet: bobblair@bobblair.austin.ibm.com
 *
 *            Extensively revised by:
 *                 John Q. Walker II, Ph.D. (JOHHQ at RALVM6)
 *                 Internet: johnq@ralvm6.vnet.ibm.com
 *
 *****************************************************************************/

/******************************************************************************
 * getopt()
 *
 * The getopt() function is a command line parser.  It returns the next
 * option character in argv that matches an option character in opstring.
 *
 * The argv argument points to an array of argc+1 elements containing argc
 * pointers to character strings followed by a null pointer.
 *
 * The opstring argument points to a string of option characters; if an
 * option character is followed by a colon, the option is expected to have
 * an argument that may or may not be separated from it by white space.
 * The external variable optarg is set to point to the start of the option
 * argument on return from getopt().
 *
 * The getopt() function places in optind the argv index of the next argument
 * to be processed.  The system initializes the external variable optind to
 * 1 before the first call to getopt().
 *
 * When all options have been processed (that is, up to the first nonoption
 * argument), getopt() returns EOF.  The special option "--" may be used to
 * delimit the end of the options; EOF will be returned, and "--" will be
 * skipped.
 *
 * The getopt() function returns a question mark (?) when it encounters an
 * option character not included in opstring.  This error message can be
 * disabled by setting opterr to zero.  Otherwise, it returns the option
 * character that was detected.
 *
 * If the special option "--" is detected, or all options have been
 * processed, EOF is returned.
 *
 * Options are marked by either a minus sign (-) or a slash (/).
 *
 * No errors are defined.
 *****************************************************************************/

#include <stdio.h>                  /* for EOF */
#include <string.h>                 /* for strchr() */


/* static (global) variables that are specified as exported by getopt() */
char *optarg = NULL;    /* pointer to the start of the option argument  */
int   optind = 1;       /* number of the next argv[] to be evaluated    */
int   opterr = 1;       /* non-zero if a question mark should be returned
                           when a non-valid option character is detected */

/* handle possible future character set concerns by putting this in a macro */
#define _next_char(string)  (char)(*(string+1))

int getopt(int argc, char *argv[], char *opstring)
{
    static char *pIndexPosition = NULL; /* place inside current argv string */
    char *pArgString = NULL;        /* where to start from next */
    char *pOptString;               /* the string in our program */


    if (pIndexPosition != NULL) {
        /* we last left off inside an argv string */
        if (*(++pIndexPosition)) {
            /* there is more to come in the most recent argv */
            pArgString = pIndexPosition;
        }
    }

    if (pArgString == NULL) {
        /* we didn't leave off in the middle of an argv string */
        if (optind >= argc) {
            /* more command-line arguments than the argument count */
            pIndexPosition = NULL;  /* not in the middle of anything */
            return EOF;             /* used up all command-line arguments */
        }

        /*---------------------------------------------------------------------
         * If the next argv[] is not an option, there can be no more options.
         *-------------------------------------------------------------------*/
        pArgString = argv[optind++]; /* set this to the next argument ptr */

        if (('/' != *pArgString) && /* doesn't start with a slash or a dash? */
            ('-' != *pArgString)) {
            --optind;               /* point to current arg once we're done */
            optarg = NULL;          /* no argument follows the option */
            pIndexPosition = NULL;  /* not in the middle of anything */
            return EOF;             /* used up all the command-line flags */
        }

        /* check for special end-of-flags markers */
        if ((strcmp(pArgString, "-") == 0) ||
            (strcmp(pArgString, "--") == 0)) {
            optarg = NULL;          /* no argument follows the option */
            pIndexPosition = NULL;  /* not in the middle of anything */
            return EOF;             /* encountered the special flag */
        }

        pArgString++;               /* look past the / or - */
    }

    if (':' == *pArgString) {       /* is it a colon? */
        /*---------------------------------------------------------------------
         * Rare case: if opterr is non-zero, return a question mark;
         * otherwise, just return the colon we're on.
         *-------------------------------------------------------------------*/
        return (opterr ? (int)'?' : (int)':');
    }
    else if ((pOptString = strchr(opstring, *pArgString)) == 0) {
        /*---------------------------------------------------------------------
         * The letter on the command-line wasn't any good.
         *-------------------------------------------------------------------*/
        optarg = NULL;              /* no argument follows the option */
        pIndexPosition = NULL;      /* not in the middle of anything */
        return (opterr ? (int)'?' : (int)*pArgString);
    }
    else {
        /*---------------------------------------------------------------------
         * The letter on the command-line matches one we expect to see
         *-------------------------------------------------------------------*/
        if (':' == _next_char(pOptString)) { /* is the next letter a colon? */
            /* It is a colon.  Look for an argument string. */
            if ('\0' != _next_char(pArgString)) {  /* argument in this argv? */
                optarg = &pArgString[1];   /* Yes, it is */
            }
            else {
                /*-------------------------------------------------------------
                 * The argument string must be in the next argv.
                 * But, what if there is none (bad input from the user)?
                 * In that case, return the letter, and optarg as NULL.
                 *-----------------------------------------------------------*/
                if (optind < argc)
                    optarg = argv[optind++];
                else {
                    optarg = NULL;
                    return (opterr ? (int)'?' : (int)*pArgString);
                }
            }
            pIndexPosition = NULL;  /* not in the middle of anything */
        }
        else {
            /* it's not a colon, so just return the letter */
            optarg = NULL;          /* no argument follows the option */
            pIndexPosition = pArgString;    /* point to the letter we're on */
        }
        return (int)*pArgString;    /* return the letter that matched */
    }
}

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