GETOPT_LONG(3) Library Functions Manual GETOPT_LONG(3)

getopt_long — get long options from command line argument list

Standard C Library (libc, -lc)

#include <getopt.h>

int
getopt_long(int argc, char * const *argv, const char *optstring, struct option *long_options, int *index);

The () function is similar to getopt(3) but it accepts options in two forms: words and characters. The getopt_long() function provides a superset of the functionality of getopt(3). getopt_long() can be used in two ways. In the first way, every long option understood by the program has a corresponding short option, and the option structure is only used to translate from long options to short options. When used in this fashion, getopt_long() behaves identically to getopt(3). This is a good way to add long option processing to an existing program with the minimum of rewriting.

In the second mechanism, a long option sets a flag in the option structure passed, or will store a pointer to the command line argument in the option structure passed to it for options that take arguments. Additionally, the long option's argument may be specified as a single argument with an equal sign, e.g.

myprogram --myoption=somevalue

When a long option is processed the call to () will return 0. For this reason, long option processing without shortcuts is not backwards compatible with getopt(3).

It is possible to combine these methods, providing for long options processing with short option equivalents for some options. Less frequently used options would be processed as long options only.

Abbreviated long option names are accepted when () processes long options if the abbreviation is unique. An exact match is always preferred for a defined long option.

The () call requires a structure to be initialized describing the long options. The structure is:

struct option {
	char *name;
	int has_arg;
	int *flag;
	int val;
};

The name field should contain the option name without the leading double dash.

The has_arg field should be one of:

no argument to the option is expected.
an argument to the option is required.
an argument to the option may be presented.

If flag is not NULL, then the integer pointed to by it will be set to the value in the val field. If the flag field is NULL, then the val field will be returned. Setting flag to NULL and setting val to the corresponding short option will make this function act just like getopt(3).

If the index argument is not NULL, the integer it points to will be set to the index of the long option in the long_options array.

The last element of the long_options array has to be filled with zeroes (see EXAMPLES section).

extern char *optarg;
extern int optind;
int bflag, ch, fd;
int daggerset;

/* options descriptor */
static struct option longopts[] = {
	{ "buffy",	no_argument,		NULL, 		'b' },
	{ "fluoride",	required_argument,	NULL, 	       	'f' },
	{ "daggerset",	no_argument,		&daggerset,	1 },
	{ NULL,		0,			NULL, 		0 }
};

bflag = 0;
while ((ch = getopt_long(argc, argv, "bf:", longopts, NULL)) != -1)
	switch (ch) {
	case 'b':
		bflag = 1;
		break;
	case 'f':
		if ((fd = open(optarg, O_RDONLY, 0)) < 0) {
			(void)fprintf(stderr,
			    "myname: %s: %s\n", optarg, strerror(errno));
			exit(1);
		}
		break;
	case 0:
		if(daggerset) {
			fprintf(stderr,"Buffy will use her dagger to "
				       "apply fluoride to dracula's teeth\n");
		}
		break;
	case '?':
	default:
		usage();
}
argc -= optind;
argv += optind;

This section describes differences to the GNU implementation found in glibc-2.1.3:

handling of - as first char of option string in presence of environment variable POSIXLY_CORRECT:
ignores POSIXLY_CORRECT and returns non-options as arguments to option '\1'.
honors POSIXLY_CORRECT and stops at the first non-option.
handling of :: in options string in presence of POSIXLY_CORRECT:
GNU and NetBSD ignore POSIXLY_CORRECT here and take :: to mean the preceding option takes an optional argument.
return value in case of missing argument if first character (after + or -) in option string is not ':':
returns '?'
NetBSD
returns ':' (since NetBSD's getopt does).
handling of --a in getopt:
parses this as option '-', option 'a'.
parses this as '--', and returns -1 (ignoring the a). (Because the original getopt does.)
setting of optopt for long options with flag != NULL:
sets optopt to val.
sets optopt to 0 (since val would never be returned).
handling of -W with W; in option string in getopt (not getopt_long):
causes a segfault.
returns -1, with optind pointing past the argument of -W (as if `-W arg' were `--arg', and thus '--' had been found).
setting of optarg for long options without an argument that are invoked via -W (W; in option string):
sets optarg to the option name (the argument of -W).
sets optarg to NULL (the argument of the long option).
handling of -W with an argument that is not (a prefix to) a known long option (W; in option string):
returns -W with optarg set to the unknown option.
treats this as an error (unknown option) and returns '?' with optopt set to 0 and optarg set to NULL (as GNU's man page documents).
The error messages are different.
NetBSD does not permute the argument vector at the same points in the calling sequence as GNU does. The aspects normally used by the caller (ordering after -1 is returned, value of optind relative to current positions) are the same, though. (We do fewer variable swaps.)

getopt(3)

The getopt_long() function first appeared in GNU libiberty. The first NetBSD implementation appeared in 1.5.

The implementation can completely replace getopt(3), but right now we are using separate code.

The argv argument is not really const.

December 9, 2018 NetBSD 11.0