NAME
getopt_long —
get long options from
command line argument list
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <getopt.h>
int
getopt_long(
int
argc,
char * const
*argv,
const char
*optstring,
struct option
*long_options,
int
*index);
DESCRIPTION
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 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.
Abbreviated long option names are accepted when
getopt_long()
processes long options if the abbreviation is unique. An exact match is always
preferred for a defined long option.
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 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 field 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).
EXAMPLES
extern char *optarg;
extern int optind;
int bflag, ch, fd;
int daggerset;
/* options descriptor */
static struct option longopts[] = {
{ "buffy", no_argument, 0, 'b' },
{ "fluoride", required_argument, 0, '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;
IMPLEMENTATION DIFFERENCES
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.)
SEE ALSO
getopt(3)
HISTORY
The
getopt_long() function first appeared in GNU libiberty.
The first
NetBSD implementation appeared in 1.5.
BUGS
The implementation can completely replace
getopt(3), but right now we are
using separate code.
The
argv argument is not really const.