Handling Command Line arguments.. (with getopt)

Normally, getopt is called in a loop. When getopt returns -1, indicating no more options are present, the loop terminates.

A switch statement is used to dispatch on the return value from getopt. In typical use, each case just sets a variable that is used later in the program.

A second loop is used to process the remaining non-option arguments.

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int
main (int argc, char **argv)
{
int aflag = 0;
int bflag = 0;
char *cvalue = NULL;
int index;
int c;

opterr = 0;

while ((c = getopt (argc, argv, "abc:")) != -1)
switch (c)
{
case 'a':
aflag = 1;
break;
case 'b':
bflag = 1;
break;
case 'c':
cvalue = optarg;
break;
case '?':
if (optopt == 'c')
fprintf (stderr, "Option -%c requires an argument.\n", optopt);
else if (isprint (optopt))
fprintf (stderr, "Unknown option `-%c'.\n", optopt);
else
fprintf (stderr,
"Unknown option character `\\x%x'.\n",
optopt);
return 1;
default:
abort ();
}

printf ("aflag = %d, bflag = %d, cvalue = %s\n",
aflag, bflag, cvalue);

for (index = optind; index < argc; index )
printf ("Non-option argument %s\n", argv[index]);
return 0;
}

Compile :

g++ testopt.cpp -o testopt

Run with various arguments:

% testopt

aflag = 0, bflag = 0, cvalue = (null)

% testopt -ab

     aflag = 1, bflag = 1, cvalue = (null)      

     % testopt -ab -c hello

     aflag = 1, bflag = 1, cvalue = hello