Parse to integer with argp.h - c

Question

I would like to be able to receive program arguments and options in my C program. The options should be treated as floats or ints. For some reason, I couldn't find good articles, tutorials, docs about argp.h. I started my implementation with the examples on the GNU Libc Manual, though unfortunately, it didn't get me to the solution.
Here is how I tried to solve the problem (example can be compiled, included every necessary line):
#include <stdlib.h>
#include <argp.h>
static char doc[] = "Doc";
static char args_doc[] = "ARG1";
static struct argp_option options[] = {
{"bool", 'b', 0, 0, "Simple boolean flag, works as I expected."},
{"int", 'i', 0, 0, "Would like to be able to parse options as --int=4 or -i 4."}, // but I can't
{0}
};
struct arguments {char *args[1]; int xbool, xint;};
static error_t
parse_opt (int key, char *arg, struct argp_state *state) {
struct arguments *arguments = state->input;
printf("key = %c, arg = %s\n", key, arg); // My attempt to understand the problem
//if (arg == NULL) return 0; // Prevents segfaults, in order to see how the args and keys change
switch (key) {
case 'b': arguments->xbool = 1; break;
case 'i': arguments->xint = (int) strtol(arg, NULL, 10); break;
case ARGP_KEY_ARG: if (state->arg_num >= 1) {argp_usage(state);} arguments->args[state->arg_num] = arg; break;
case ARGP_KEY_END: if (state->arg_num < 1) {argp_usage(state);} break;
default: return ARGP_ERR_UNKNOWN;
}
return 0;
}
static struct argp argp = { options, parse_opt, args_doc, doc };
int main (int argc, char **argv) {
struct arguments arguments;
arguments.xbool = 0;
arguments.xint = 0;
argp_parse (&argp, argc, argv, 0, 0, &arguments);
printf("ARG1 = %s\nbool option = %s\nparsed int option = %d",
arguments.args[0], arguments.xbool ? "true" : "false", arguments.xint);
exit (0);
}
The simple boolean flag works, as expected, so ./myprogram.out myarg --bool and ./myprogram.out myarg -b changes the flag's value.
However, I can't seem to find a way to parse the arguments as integers or floating point numbers.
This it the output I get for ./a.out -b --int=2 myarg:
key = , arg = (null)
key = b, arg = (null)
./a.out: option '--int' doesn't allow an argument
Try `a.out --help' or `a.out --usage' for more information.
and for ./a.out -b --int 2 myarg I get a segmentation fault, as I try to parse a NULL: key = i, arg = (null). I added a NULL check, and this way I could see, that the option I would like to parse comes with a , key (expected to come with i).
key = i, arg = (null)
key = , arg = 2
I thought about using a library because the program needs to handle various float and int options, falling back to default values, and I've seen often that it's not recommended to roll your own argument and options parser. Based on the examples, argp.h looked promising, however I couldn't get it to work yet.
ps. I know that parsing directly to ints and floats are not part of argp, this is why I was (naively, it seems) trying to add it to the structures and parse_opt function.

Answer 1

As it turned out, there was an error with options[]. The third, const char *arg parameter in the argp_option struct must be provided, if the option has argument associated with it [source: GNU C: Argp Option Vectors].
static struct argp_option options[] = {
{"bool", 'b', 0, 0, "Simple boolean flag, works as I expected."},
{"int", 'i', "Numbah", 0, "Now everything works as expected, I get the correct key-value (key-arg) pair in the parse_opt function"},
{0}
};