Correct or decent getopts_long usage? - c

Question

What it the correct usage if I want this behaviour:
$ ./a.out --help for printing help information
$ ./a.out --version for printing the program version
I managed to code this so that it takes the arguments but I don't know a good / correct way to separate the messages since they are the same case.
static struct option long_options[] = {
{"help", no_argument, 0, 0 },
{"version", no_argument, 0, 0 },
{0, 0, 0, 0 }
};
int main(int argc, char *argv[]) {
while (1) {
int this_option_optind = optind ? optind : 1;
int option_index = 0;
c = getopt_long(argc, argv, "",
long_options, &option_index);
if (c == -1)
break;
switch (c) {
case 0:
printf("option %s", long_options[option_index].name);
if (optarg)
printf(" with arg %s", optarg);
printf("\n");
return 0;
case '0':
case '1':
case '2':
if (digit_optind != 0 && digit_optind != this_option_optind)
printf("digits occur in two different argv-elements.\n");
digit_optind = this_option_optind;
printf("option 2 2 %c\n", c);
return 0;
case 'a':
printf("option a\n");
break;
case 'b':
printf("option b\n");
break;
case 'c':
printf("option c with value '%s'\n", optarg);
break;
case 'd':
printf("option d with value '%s'\n", optarg);
break;
case '?':
break;
default:
printf("?? getopt returned character code 0%o ??\n", c);
}
}
if (optind < argc) {
printf("non-option ARGV-elements: ");
while (optind < argc)
printf("%s ", argv[optind++]);
printf("\n");
}
...

Answer 1

Here you have an example:
while (1)
{
int option_index = 0;
static struct option long_options[] = {
{"with_param", required_argument, 0, 'p'},
{"version", no_argument, 0, 'v'},
{"help", no_argument, 0, 'h'},
{0, 0, 0, 0}
};
option = getopt_long(argc, argv, "p:vh",
long_options, &option_index);
if (option == -1)
break;
switch (option) {
case 'p':
{
store_parameter(optarg);
break;
}
case 'v':
{
print_version();
break;
}
case 'h':
{
print_help();
exit(EXIT_SUCCESS);
break;
}
default:
{
fprintf(stderr, "Error (%s): unrecognized option.\n", __FUNCTION__);
print_help();
exit(EXIT_FAILURE);
break;
}
} /* end switch */
}
Notice the string "p:vh" as parameter of getopt_long, which allows you to also use short options. (":" follows options with a required argument)

Answer 2

You need to tell getopt_long the values it has to return:
static struct option long_options[] = {
{"help", no_argument, NULL, 1 },
{"version", no_argument, NULL, 2 },
{0, 0, 0, 0 }
};
Also, you could use "-h" as a synonym to "--help" and "-V" as a synonym to "--version", this would be done this way:
static struct option long_options[] = {
{"help", no_argument, NULL, 'h' },
{"version", no_argument, NULL, 'V' },
{0, 0, 0, 0 }
};
/* ... */
c = getopt_long(argc, argv, "abc:d:Vh", long_options, &option_index);
/* ... */
case 'h': // instead of case 1:
/* ... */
case 'V': // instead of case 2:
/* ...*/