NAME
          subgetopt - get option character from command line

     SYNTAX
          #include <subgetopt.h>

          char *sgoptarg;
          int sgoptind;
          int sgoptpos;
          int sgoptdone;
          int sgoptproblem;

          int sgopt(argc,argv,opts);

          int argc;
          char **argv;
          char *opts;

     DESCRIPTION
          sgopt returns the next valid command-line option character
          from argv.

          Valid option characters are listed in the opts string.  opts
          may be empty.  A character in opts may be followed by a
          colon, in which case it takes an option argument. Avoid
          using the characters ?, :, and - as option characters.

          Below option argument is abbreviated as optarg and command-
          line argument is abbreviated as cmdarg.

          Options are listed in cmdargs which begin with a minus sign.
          Several options which do not take optargs may be combined
          into one cmdarg.

          An option which takes an optarg may be handled in two ways.
          If it appears at the very end of a cmdarg, then the entire
          next cmdarg is the optarg.  But if there are any characters
          in the cmdarg after the option character, then those
          characters form the optarg.  The optarg is returned in
          sgoptarg.  Next time sgopt looks at the cmdarg which follows
          the optarg.

          If a cmdarg does not begin with a hyphen, or if it is a lone
          hyphen not followed by any characters, or if it begins with
          two hyphens, then it terminates option processing, and sgopt
          returns an appropriate code.  If there are two hyphens,
          sgopt will advance attention to the next cmdarg, so it can
          be called again to read further options.

     PROPER USAGE
          sgoptproblem should be used only when sgopt returns ?.
          sgoptind and sgoptpos are defined all the time.  sgoptarg is
          defined all the time; it is null unless sgopt has just
          returned an option with optarg.

          sgopt is typically used as follows.

          #include <subgetopt.h>

          main(argc,argv) int argc; char **argv; { int opt;

          while ((opt = sgopt(argc,argv,"a:s")) != sgoptdone)
            switch(opt) {
              case 'a':
                printf("opt a with optarg %s\n",sgoptarg); break;
              case 's':
                printf("opt s with no optarg\n"); break;
              case '?':
                if (argv[sgoptind] && (sgoptind < argc))
                  printf("illegal opt %c\n",sgoptproblem);
                else
                  printf("missing arg, opt %c\n",sgoptproblem);
                exit(1);
            }

          argv += sgoptind;
          while (*argv) printf("argument %s\n",*argv++);
          exit(0);
          }

          The end of the command line is marked by either argc, or a
          null pointer in argv, whichever comes first.  Normally these
          two markers coincide, so it is redundant to test for both
          argv[sgoptind] and sgoptind < argc. The above code shows
          both tests as an illustration.

          Multiple option sets: One useful technique is to call sgopt
          with a primary opts until it returns EOF, then call sgopt
          with a secondary opts until it returns EOF.  The user can
          provide primary options, then a double hyphen, and then
          secondary options.  No special handling is needed if some or
          all of the options are omitted.  The same technique can be
          used for any number of option sets in series.

          Multiple command lines: Before parsing a new argv, make sure
          to set sgoptind and sgoptpos back to 1 and 0.

     PARSING STAGES
          sgopt keeps track of its position in argv with sgoptind and
          sgoptpos, which are initialized to 1 and 0.  It looks at
          argv[sgoptind][sgoptpos] and following characters.

          sgopt indicates that no more options are available by
          returning sgoptdone, which is initialized to SUBGETOPTDONE,
          which is defined as -1.

          sgopt begins by setting optarg to null.

          Ending conditions: If argv is null, or sgoptind is larger
          than argc, or the current cmdarg argv[sgoptind] is null,
          then sgopt returns optdone.

          Stage one: If the current character is zero, sgopt moves to
          the beginning of the next cmdarg.  It then checks the ending
          conditions again.

          Stage two: If the current position is the begining of the
          cmdarg, sgopt checks whether the current character is a
          minus sign.  If not it returns optdone.  It then moves to
          the next character.  If that character is zero, sgopt moves
          back to the beginning of the cmdarg, and returns sgoptdone.
          If the character is a minus sign, sgopt moves to the
          beginning of the next cmdarg, and returns sgoptdone.

          Stage three: sgopt records the current character, c, and
          moves to the next character.  There are three possibilities:
          (1) c is an option character without optarg in opts, or (2)
          c is an option character with optarg in opts, or (3) c does
          not appear in opts.

          (1) If c appears as an option character without optarg in
          opts, sgopt returns c.

          (2) If c appears as an option character with optarg in opts,
          sgopt sets sgoptarg to the current position, and moves to
          the next cmdarg.  If sgoptarg is nonempty, sgopt returns c.

          Then sgopt sets sgoptarg to the current cmdarg.  If the
          current cmdarg is null, or past argc, sgopt sets
          sgoptproblem to c and returns ?.  Otherwise sgopt moves to
          the next argument and returns c.

          (2) If c does not appear in opts, sgopt sets sgoptproblem to
          c and returns ?.

     SYNTAX NOTE
          sgopt is actually a macro abbreviation for subgetopt.  The
          external sg variables are also macros for subget.  These
          macros are defined in <subgetopt.h>, unless SUBGETOPTNOSHORT
          is defined when <subgetopt.h> is included.

     VERSION
          subgetopt version 0.9, 931129.

     AUTHOR
          Placed into the public domain by Daniel J. Bernstein.