/* This program uses the same features as example 2, and uses options and
        arguments.
     
        We now use the first four fields in ARGP, so here's a description of them:
          OPTIONS  -- A pointer to a vector of struct argp_option (see below)
          PARSER   -- A function to parse a single option, called by argp
          ARGS_DOC -- A string describing how the non-option arguments should look
          DOC      -- A descriptive string about this program; if it contains a
                      vertical tab character (\v), the part after it will be
                      printed *following* the options
     
        The function PARSER takes the following arguments:
          KEY  -- An integer specifying which option this is (taken
                  from the KEY field in each struct argp_option), or
                  a special key specifying something else; the only
                  special keys we use here are ARGP_KEY_ARG, meaning
                  a non-option argument, and ARGP_KEY_END, meaning
                  that all arguments have been parsed
          ARG  -- For an option KEY, the string value of its
                  argument, or NULL if it has none
          STATE-- A pointer to a struct argp_state, containing
                  various useful information about the parsing state; used here
                  are the INPUT field, which reflects the INPUT argument to
                  argp_parse, and the ARG_NUM field, which is the number of the
                  current non-option argument being parsed
        It should return either 0, meaning success, ARGP_ERR_UNKNOWN, meaning the
        given KEY wasn't recognized, or an errno value indicating some other
        error.
     
        Note that in this example, main uses a structure to communicate with the
        parse_opt function, a pointer to which it passes in the INPUT argument to
        argp_parse.  Of course, it's also possible to use global variables
        instead, but this is somewhat more flexible.
     
        The OPTIONS field contains a pointer to a vector of struct argp_option's;
        that structure has the following fields (if you assign your option
        structures using array initialization like this example, unspecified
        fields will be defaulted to 0, and need not be specified):
          NAME   -- The name of this option's long option (may be zero)
          KEY    -- The KEY to pass to the PARSER function when parsing this option,
                    *and* the name of this option's short option, if it is a
                    printable ascii character
          ARG    -- The name of this option's argument, if any
          FLAGS  -- Flags describing this option; some of them are:
                      OPTION_ARG_OPTIONAL -- The argument to this option is optional
                      OPTION_ALIAS        -- This option is an alias for the
                                             previous option
                      OPTION_HIDDEN       -- Don't show this option in --help output
          DOC    -- A documentation string for this option, shown in --help output
     
        An options vector should be terminated by an option with all fields zero. */
     
     #include <stdlib.h>
     #include <argp.h>
     
     const char *argp_program_version =
       "argp-ex3 1.0";
     const char *argp_program_bug_address =
       "<bug-gnu-utils@gnu.org>";
     
     /* Program documentation. */
     static char doc[] =
       "Argp example #3 -- a program with options and arguments using argp";
     
     /* A description of the arguments we accept. */
     static char args_doc[] = "ARG1 ARG2";
     
     /* The options we understand. */
     static struct argp_option options[] = {
       {"verbose",  'v', 0,      0,  "Produce verbose output" },
       {"quiet",    'q', 0,      0,  "Don't produce any output" },
       {"silent",   's', 0,      OPTION_ALIAS },
       {"output",   'o', "FILE", 0,
        "Output to FILE instead of standard output" },
       { 0 }
     };
     
     /* Used by main to communicate with parse_opt. */
     struct arguments
     {
       char *args[2];                /* arg1 & arg2 */
       int silent, verbose;
       char *output_file;
     };
     
     /* Parse a single option. */
     static error_t
     parse_opt (int key, char *arg, struct argp_state *state)
     {
       /* Get the input argument from argp_parse, which we
          know is a pointer to our arguments structure. */
       struct arguments *arguments = state->input;
     
       switch (key)
         {
         case 'q': case 's':
           arguments->silent = 1;
           break;
         case 'v':
           arguments->verbose = 1;
           break;
         case 'o':
           arguments->output_file = arg;
           break;
     
         case ARGP_KEY_ARG:
           if (state->arg_num >= 2)
             /* Too many arguments. */
             argp_usage (state);
     
           arguments->args[state->arg_num] = arg;
     
           break;
     
         case ARGP_KEY_END:
           if (state->arg_num < 2)
             /* Not enough arguments. */
             argp_usage (state);
           break;
     
         default:
           return ARGP_ERR_UNKNOWN;
         }
       return 0;
     }
     
     /* Our argp parser. */
     static struct argp argp = { options, parse_opt, args_doc, doc };
     
     int
     main (int argc, char **argv)
     {
       struct arguments arguments;
     
       /* Default values. */
       arguments.silent = 0;
       arguments.verbose = 0;
       arguments.output_file = "-";
     
       /* Parse our arguments; every option seen by parse_opt will
          be reflected in arguments. */
       argp_parse (&argp, argc, argv, 0, 0, &arguments);
     
       printf ("ARG1 = %s\nARG2 = %s\nOUTPUT_FILE = %s\n"
               "VERBOSE = %s\nSILENT = %s\n",
               arguments.args[0], arguments.args[1],
               arguments.output_file,
               arguments.verbose ? "yes" : "no",
               arguments.silent ? "yes" : "no");
     
       exit (0);
     }