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 getopt_long() function is similar to getopt(3) but it accepts options
in two forms: words and characters. The getopt_long() function provides a
superset of 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 getopt_long() 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.
The getopt_long() 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 no argument to the option is expect.
required_argument an argument to the option is required.
optional_argument an argument to the option may be presented.
If flag is non-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).
extern char *optarg;
extern int optind;
int bflag, ch, fd;
int daggerset;
/* options descriptor */
static struct option longopts[] = {
{ "buffy", no_argument, 0, 'b' },
{ "floride", required_argument, 0, 'f' },
{ "daggerset", no_argument, daggerset, 1 },
{ 0, 0, 0, 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 floride to dracula's teeth\n");
}
break;
case '?':
default:
usage();
}
argc -= optind;
argv += optind;
IMPLEMENTATION DIFFERENCES [Toc] [Back] This section describes differences to the GNU implementation found in
glibc-2.1.3:
o handling of - as first char of option string in presence of environment
variable POSIXLY_CORRECT:
GNU ignores POSIXLY_CORRECT and returns non-options as arguments
to option '\1'.
NetBSD honors POSIXLY_CORRECT and stops at the first non-option.
o handling of :: in options string in presence of POSIXLY_CORRECT:
Both GNU and NetBSD ignore POSIXLY_CORRECT here and take :: to
mean the preceding option takes an optional argument.
o return value in case of missing argument if first character (after +
or -) in option string is not ':':
GNU returns '?'
NetBSD returns ':' (since NetBSD's getopt does).
o handling of --a in getopt:
GNU parses this as option '-', option 'a'.
NetBSD parses this as '--', and returns -1 (ignoring the a).
(Because the original getopt does.)
o setting of optopt for long options with flag != NULL:
GNU sets optopt to val.
NetBSD sets optopt to 0 (since val would never be returned).
o handling of -W with W; in option string in getopt (not getopt_long):
GNU causes a segfault.
NetBSD returns -1, with optind pointing past the argument of -W (as
if `-W arg' were `--arg', and thus '--' had been found).
o setting of optarg for long options without an argument that are
invoked via -W (W; in option string):
GNU sets optarg to the option name (the argument of -W).
NetBSD sets optarg to NULL (the argument of the long option).
o handling of -W with an argument that is not (a prefix to) a known
long option (W; in option string):
GNU returns -W with optarg set to the unknown option.
NetBSD 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).
o The error messages are different.
o 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 completelely replace getopt(3), but right now we
are using separate code.
BSD April 1, 2000 BSD
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