说明

Argp一般是GNU C用来处理程序参数的接口函数。

Argp provides features unavailable in the more commonly used getopt interface. These features include automatically producing output in response to the ‘–help’ and ‘–version’ options, as described in the GNU coding standards. Using argp makes it less likely that programmers will neglect to implement these additional options or keep them up to date.

Argp also provides the ability to merge several independently defined option parsers into one, mediating conflicts between them and making the result appear seamless. A library can export an argp option parser that user programs might employ in conjunction with their own option parsers, resulting in less work for the user programs. Some programs may use only argument parsers exported by libraries, thereby achieving consistent and efficient option-parsing for abstractions implemented by the libraries.

实例

  /* 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
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";
"<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);
}

Written on May 1, 2014