getopt_long() function with custom argc and argv

Question

I am having trouble using getopt_long() function with custom argc and argv.

I receive my arguments in a string instead of the real command line args. Then a new_argc and new_argv was built from this string to be used with getopt_long(). But getopt_long() fails on the first call itself. returns EOF and optarg = NULL.

string is "-c 10.30.99.41" 
new_argc = 3
new_argv[0]=>./prog_name
new_argv[1]=>-c
new_argv[2]=>10.30.99.41

getopt_long works OK for me if I pass command line args. So my short and long options are correct. But if I pass the new_argc and new_argv it fails.

I am sure my short and long options are right and the argv is NULL terminated. I apologize I cant post more code here.

I doubt if getopt_long can be used with a custom argc and argv. I suspect it works only with a real argc and argv because it must be referencing some other code in libc related to argc,argv. Any comments?

option = getopt_long( new_argc, new_argv, short_options, long_options, NULL );

Are you going to post what the string is and how it is being used to build the list? — Random832, Oct 28 '11 at 16:11
@anoop, what about the `optstring` argument? Can you post the code that calls `getopt_long()`? — Frédéric Hamidi, Oct 28 '11 at 16:26
I've no idea if this will make a difference, but `new_argv[4]` should be 0 if you want to simulate how `main()` is really called. — Alan Stokes, Oct 28 '11 at 16:45
@anoop That would have been more obvious if you'd just showed the real code. — Alan Stokes, Oct 29 '11 at 10:51

nos · Accepted Answer · 2011-10-28T17:15:38.593

EDIT:

"The variable optind is the index of the next element to be processed in argv. The system initializes this value to 1. The caller can reset it to 1 to restart scanning of the same argv, or when scanning a new argument vector."

So, yes. You can use getopt_long to scan the arguments or another argument list again. However, if someone has called getopt_long previously, you have to set the global optind variable to back to 1.

Remember that the argv in main() is NULL terminated and argc long, that is; argv[argc] == NULL. So you likely have to make sure the last element in your own new_argv is a NULL pointer.

(Note, please show all the relevant code when posting, it's hard to guess what the error is, e.g. showing what short_options, long_option is, how you actually build your new_argv, variable declarations etc.)

Hit the nail on the head man, thanks, much appreciated. optind = 0 or 1 fixes it. getopt_long was used earlier. — n00pster, Oct 28 '11 at 17:32

getopt_long() function with custom argc and argv

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