Read man getopt
http://linux.die.net/man/3/getopt
optstring is a string containing the legitimate option characters. If such a character is followed by a colon, the option requires an argument, so getopt() places a pointer to the following text in the same argv-element, or the text of the following argv-element, in optarg. Two colons mean an option takes an optional arg; if there is text in the current argv-element (i.e., in the same word as the option name itself, for example, "-oarg"), then it is returned in optarg, otherwise optarg is set to zero.
A sample code:
#include <stdio.h>
#include <unistd.h>
int main (int argc, char *argv[])
{
int opt;
while ((opt = getopt (argc, argv, "i:o:")) != -1)
{
switch (opt)
{
case 'i':
printf("Input file: \"%s\"\n", optarg);
break;
case 'o':
printf("Output file: \"%s\"\n", optarg);
break;
}
}
return 0;
}
Here in the optstring
is "i:o:" the colon ':' character after each character in the string tells that those options will require an argument. You can find argument as a string in the optarg
global var. See manual for detail and more examples.
For more than one character option switches, see the long options getopt_long
. Check the manual for examples.
EDIT in response to the single '-' long options:
From the man pages
getopt_long_only() is like getopt_long(), but '-' as well as "--" can indicate a long option. If an option that starts with '-' (not "--") doesn't match a long option, but does match a short option, it is parsed as a short option instead.
Check the manual and try it.