GETOPT_LONG(3) | Library Functions Manual | GETOPT_LONG(3) |
getopt_long
,
getopt_long_only
— get long
options from command line argument list
Standard C Library (libc, -lc)
#include
<getopt.h>
extern char *optarg;
extern int optind;
extern int optopt;
extern int opterr;
extern int optreset;
int
getopt_long
(int argc,
char * const *argv, const char
*optstring, const struct option *longopts,
int *longindex);
int
getopt_long_only
(int argc,
char * const *argv, const char
*optstring, const struct option *longopts,
int *longindex);
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). The
getopt_long
() function 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
required_argument
optional_argument
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 longindex field is not
NULL
, then the integer pointed to by it will be set
to the index of the long option relative to
longopts.
The last element of the longopts array has to be filled with zeroes.
The
getopt_long_only
()
function behaves identically to getopt_long
() with
the exception that long options may start with
‘-
’ in addition to
‘--
’. If an option starting with
‘-
’ does not match a long option but
does match a single-character option, the single-character option is
returned.
If the flag field in struct
option is NULL
,
getopt_long
() and
getopt_long_only
() return the value specified in the
val field, which is usually just the corresponding
short option. If flag is not
NULL
, these functions return 0 and store
val in the location pointed to by
flag.
These functions return ‘:
’
if there was a missing option argument and error messages are suppressed,
‘?
’ if the user specified an unknown
or ambiguous option, and -1 when the argument list has been exhausted. The
default behavior when a missing option argument is encountered is to write
an error and return ‘?
’. Specifying
‘:
’ in optstr
will cause the error message to be suppressed and
‘:
’ to be returned instead.
In addition to ‘:
’, a
leading ‘+
’ or
‘-
’ in optstr
also has special meaning. If either of these are specified, they must appear
before ‘:
’.
A leading ‘+
’ indicates that
processing should be halted at the first non-option argument, matching the
default behavior of getopt(3). The
default behavior without ‘+
’ is to
permute non-option arguments to the end of argv.
A leading ‘-
’ indicates that
all non-option arguments should be treated as if they are arguments to a
literal ‘1
’ flag (i.e., the function
call will return the value 1, rather than the char literal '1').
POSIXLY_CORRECT
-
’ or
‘+
’ in the
optstring is ignored.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)) == -1) err(1, "unable to open %s", optarg); break; case 0: if (daggerset) { fprintf(stderr,"Buffy will use her dagger to " "apply fluoride to dracula's teeth\n"); } break; default: usage(); } } argc -= optind; argv += optind;
This section describes differences to the GNU implementation found in glibc-2.1.3:
NULL
:
-W
’
(‘W;
’ in option string):
-W
’).NULL
(the
argument of the long option).-W
’ with an argument
that is not (a prefix to) a known long option
(‘W;
’ in option string):
-W
’ with
optarg set to the unknown option.?
’ with
optopt set to 0 and optarg
set to NULL
(as GNU's man page
documents).The getopt_long
() and
getopt_long_only
() functions first appeared in the
GNU libiberty library. The first BSD implementation
of getopt_long
() appeared in NetBSD
1.5, the first BSD implementation of
getopt_long_only
() in OpenBSD
3.3. FreeBSD first included
getopt_long
() in FreeBSD
5.0, getopt_long_only
() in
FreeBSD 5.2.
The argv argument is not really
const as its elements may be permuted (unless
POSIXLY_CORRECT
is set).
The implementation can completely replace getopt(3), but right now we are using separate code.
getopt_long
makes the assumption that the
first argument should always be skipped because it's typically the program
name. As a result, setting optind to 0 will indicate
that getopt_long
should reset, and
optind will be set to 1 in the process. This behavior
differs from getopt(3), which will
handle an optind value of 0 as expected and process
the first element.
December 24, 2022 | macOS 14.6 |