Getopt- Passing string parameter for argument - c

Question

I have a program which takes in multiple command line arguments so I am using getopt. One of my arguments takes in a string as a parameter. Is there anyway to obtain that string through the getopt function or would I have to obtain it through the argv[] array? Also can getopt read args like -file ? All the arguments I have seen till now have only one character such as -a
EDIT
From the below answers I have written a program to use getopt_long(), but the switch statement only recognizes the argument when I use the character argument and not the long argument. I'm not sure why this happening. On passing the arguments -mf -file sample I do not see the print statements.
EDIT
I tried entering the command arguments as --file and then it worked. Is it not possible to do this with just -file ?
static struct option long_options[] =
{
{"mf", required_argument, NULL, 'a'},
{"md", required_argument, NULL, 'b'},
{"mn", required_argument, NULL, 'c'},
{"mw", required_argument, NULL, 'd'},
{"lf", required_argument, NULL, 'e'},
{"ld", required_argument, NULL, 'f'},
{"ln", required_argument, NULL, 'g'},
{"lw", required_argument, NULL, 'h'},
{"rf", required_argument, NULL, 'i'},
{"rd", required_argument, NULL, 'j'},
{"rn", required_argument, NULL, 'k'},
{"rw", required_argument, NULL, 'l'},
{"df", required_argument, NULL, 'm'},
{"dd", required_argument, NULL, 'n'},
{"dn", required_argument, NULL, 'o'},
{"dw", required_argument, NULL, 'p'},
{"file", required_argument, NULL, 'q'},
{NULL, 0, NULL, 0}
};
int ch=0;
while ((ch = getopt_long(argc, argv, "abcdefghijklmnopq:", long_options, NULL)) != -1)
{
// check to see if a single character or long option came through
switch (ch){
case 'a':
cout<<"title";
break;
case 'b':
break;
case 'c':
break;
case 'd':
break;
case 'e':
break;
case 'f':
break;
case 'g':
break;
case 'h':
break;
case 'i':
break;
case 'j':
break;
case 'k':
break;
case 'l':
break;
case 'm':
break;
case 'n':
break;
case 'o':
break;
case 'p':
break;
case 'q':
cout<<"file";
break;
case '?':
cout<<"wrong message"
break;
}
}

Answer 1

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.

Answer 2

To specify that a flag requires an argument, add a ':' right after the flag in the short_opt variable. To use long arguments, use getopt_long().
Here is a quick example program:
#include <getopt.h>
#include <stdio.h>
int main(int argc, char * argv[]);
int main(int argc, char * argv[])
{
int c;
const char * short_opt = "hf:";
struct option long_opt[] =
{
{"help", no_argument, NULL, 'h'},
{"file", required_argument, NULL, 'f'},
{NULL, 0, NULL, 0 }
};
while((c = getopt_long(argc, argv, short_opt, long_opt, NULL)) != -1)
{
switch(c)
{
case -1: /* no more arguments */
case 0: /* long options toggles */
break;
case 'f':
printf("you entered \"%s\"\n", optarg);
break;
case 'h':
printf("Usage: %s [OPTIONS]\n", argv[0]);
printf(" -f file file\n");
printf(" -h, --help print this help and exit\n");
printf("\n");
return(0);
case ':':
case '?':
fprintf(stderr, "Try `%s --help' for more information.\n", argv[0]);
return(-2);
default:
fprintf(stderr, "%s: invalid option -- %c\n", argv[0], c);
fprintf(stderr, "Try `%s --help' for more information.\n", argv[0]);
return(-2);
};
};
return(0);
}