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The GNU C Library

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25.3.11.3 A Program Using Argp with User Options

This program uses the same features as example 2, adding user options and arguments.

We now use the first four fields in argp (see section 25.3.3 Specifying Argp Parsers) and specify parse_opt as the parser function. See section 25.3.5 Argp Parser Functions.

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. See section 25.3 Parsing Program Options with Argp. It is retrieved by parse_opt through the input field in its state argument. See section 25.3.5.3 Argp Parsing State. Of course, it's also possible to use global variables instead, but using a structure like this is somewhat more flexible and clean.

 
/* Argp example #3 -- a program with options and arguments using argp */

/* 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 <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);
}


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