Example of Getopt (The GNU C Library)

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25.2.2 Example of Parsing Arguments with `getopt`

Here is an example showing how getopt is typically used. The key points to notice are:

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;
}

Here are some examples showing what this program prints with different combinations of arguments:

% testopt
aflag = 0, bflag = 0, cvalue = (null)
% testopt -a -b
aflag = 1, bflag = 1, cvalue = (null)
% testopt -ab
aflag = 1, bflag = 1, cvalue = (null)
% testopt -c foo
aflag = 0, bflag = 0, cvalue = foo
% testopt -cfoo
aflag = 0, bflag = 0, cvalue = foo
% testopt arg1
aflag = 0, bflag = 0, cvalue = (null)
Non-option argument arg1
% testopt -a arg1
aflag = 1, bflag = 0, cvalue = (null)
Non-option argument arg1
% testopt -c foo arg1
aflag = 0, bflag = 0, cvalue = foo
Non-option argument arg1
% testopt -a -- -b
aflag = 1, bflag = 0, cvalue = (null)
Non-option argument -b
% testopt -a -
aflag = 1, bflag = 0, cvalue = (null)
Non-option argument -

Next: Parsing Long Options with getopt_long, Previous: Using the getopt function, Up: Parsing program options using getopt [Contents][Index]