understanding getopt_long()'s hasarg setting

[ff0000]

Hi everyone,

Preamble: i'm a newbie :-)
I've a doubt about the behaviour of variable "hasarg" in the option
struct (from getopt(3)):

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

has_arg
is: no_argument (or 0) if the option does not take an
argument;
required_argume nt (or 1) if the option requires an
argument; or
optional_argume nt (or 2) if the option takes an
optional argu-
ment.

Reading this i expect that an option set with "optional_argum ent"
could get or not an
argument, but proprably i'm wrong...
I take longopt.c example from GNU libc source and i add one option,
here's the diff:

ff0000@tsi00588 pc:tmp$ diff ./glibc-2.6.1/manual/examples/longopt.c
longopt.c
27a28

{"crates", optional_argume nt, 0, 'C'},

34c35
< c = getopt_long (argc, argv, "abc:d:f:",
---

c = getopt_long (argc, argv, "abc:d:f:C: ",

64a66,69

case 'C':
printf ("option -C with value `%s'\n", optarg);
break;
>

Building it:

ff0000@tsi00588 pc:tmp$ gcc -Wall -Werror -o longopt longopt.c
ff0000@tsi00588 pc:tmp$

Testing "-C" option with and without argument:

ff0000@tsi00588 pc:tmp$ ./longopt -C 1
option -C with value `1'
ff0000@tsi00588 pc:tmp$ ./longopt -C
../longopt: option requires an argument -- C
ff0000@tsi00588 pc:tmp$

Why in the latter case it tells me that the option *requires* an
argument
even if it's set to "optional_argum ent"?
It behaves like a "required_argum ent"' s option:

ff0000@tsi00588 pc:tmp$ ./longopt -c
../longopt: option requires an argument -- c
ff0000@tsi00588 pc:tmp$

Another one: is it normal that an option's argument could be another
option?

ff0000@tsi00588 pc:tmp$ ./longopt -c -c
option -c with value `-c'
ff0000@tsi00588 pc:tmp$

?

Thanks a lot.
ff0000

[Ben Bacarisse]

Re: understanding getopt_long()'s hasarg setting

ff0000 <ff0000.it@gmai l.comwrites:

Preamble: i'm a newbie :-)

This question would have been better in comp.unix.progr ammer. You'd
hit a wider pool of people who know getopt_long -- it is not standard
C. I've set followup-to that group.

I've a doubt about the behaviour of variable "hasarg" in the option
struct (from getopt(3)):
>
struct option {
const char *name;
int has_arg;
int *flag;
int val;
};

<snip>

{"crates", optional_argume nt, 0, 'C'},

<snip>

c = getopt_long (argc, argv, "abc:d:f:C: ",

<snip>

case 'C':
printf ("option -C with value `%s'\n", optarg);
break;

has_arg affects only the long version permitting '--crates' and
'--crates=value'. As a GNU extension you can use double :: to extend
the optional nature of an argument to the single-letter form, but
optional arguments never just *follow* a single letter flag, they come
from the rest of the argument. So using:

c = getopt_long (argc, argv, "abc:d:f:C: :", ...)

the user can write both '-C' and '-Cvalue', but '-Ca' will be taken as
--crates=a and not as -C -a.

--
Ben.