Hi. I'm studying how to robustly use command line arguments and have found some good examples using getopt_long on the Web. I am looking at this example I found at:
Getopt Long Option Example (The GNU C Library)
Getopt Long Option Example (The GNU C Library)
www.gnu.org
Code:
#include <stdio.h>
#include <stdlib.h>
#include <getopt.h>
/* Flag set by ‘--verbose’. */
static int verbose_flag;
int
main (int argc, char **argv)
{
int c;
while (1)
{
static struct option long_options[] =
{
/* These options set a flag. */
{"verbose", no_argument, &verbose_flag, 1},
{"brief", no_argument, &verbose_flag, 0},
/* These options don’t set a flag.
We distinguish them by their indices. */
{"add", no_argument, 0, 'a'},
{"append", no_argument, 0, 'b'},
{"delete", required_argument, 0, 'd'},
{"create", required_argument, 0, 'c'},
{"file", required_argument, 0, 'f'},
{0, 0, 0, 0}
};
/* getopt_long stores the option index here. */
int option_index = 0;
c = getopt_long (argc, argv, "abc:d:f:",
long_options, &option_index);
/* Detect the end of the options. */
if (c == -1)
break;
switch (c)
{
case 0:
/* If this option set a flag, do nothing else now. */
if (long_options[option_index].flag != 0)
break;
printf ("option %s", long_options[option_index].name);
if (optarg)
printf (" with arg %s", optarg);
printf ("\n");
break;
case 'a':
puts ("option -a\n");
break;
case 'b':
puts ("option -b\n");
break;
case 'c':
printf ("option -c with value `%s'\n", optarg);
break;
case 'd':
printf ("option -d with value `%s'\n", optarg);
break;
case 'f':
printf ("option -f with value `%s'\n", optarg);
break;
case '?':
/* getopt_long already printed an error message. */
break;
default:
abort ();
}
}
/* Instead of reporting ‘--verbose’
and ‘--brief’ as they are encountered,
we report the final status resulting from them. */
if (verbose_flag)
puts ("verbose flag is set");
/* Print any remaining command line arguments (not options). */
if (optind < argc)
{
printf ("non-option ARGV-elements: ");
while (optind < argc)
printf ("%s ", argv[optind++]);
putchar ('\n');
}
exit (0);
}
Note:
{"add", no_argument, 0, 'a'},
{"append", no_argument, 0, 'b'},
{"delete", required_argument, 0, 'd'},
{"create", required_argument, 0, 'c'},
{"file", required_argument, 0, 'f'},
It teaches me pretty much everything I need to know, but I noticed it doesn't handle one situation very well.
If I enter say: ./a.out -d -a
it knows that -d requires an argument, but because that argument is missing, it takes the next option (-a) as the argument to -d (if that makes sense).
It produces output: option -d with value `-a'
For: ./a.out -a -d it outputs:
option -a
./a.out: option requires an argument -- 'd'
Is there an easy way to check that the next thing read is not in fact the next option?? Check for '-' as te first character perhaps??
Or is there a better example for parsing command line arguments that I should be studying?
Thanks.
It only reports the "option requires and argument" error message if it is the last option specified