Getopt- Passing string parameter for argument

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.