getopt

Syntax

#include <unistd.h>

int getopt(int argc, char * const *argv, const char *options);
extern char *optarg;
extern int optind, opterr;
extern char optopt;

Description

Parse options from the command line. The options are a string of valid option characters. If a given option takes a parameter, that character should be followed by a colon.

For each valid switch, this function sets optarg to the argument (if the switch takes one), sets optind to the index in argv that it is using, sets optopt to the option letter found, and returns the option letter found.

If an unexpected option is found, getopt will return ?, and if opterr is nonzero, will print an error message to stderr.

The special option -- indicates that no more options follow on the command line, and cause getopt to stop looking.

Return Value

The option found, or -1 if no more options.

Portability

not ANSI, POSIX

Example

int c;
opterr = 0;
while ((c=getopt(argc, argv, "vbf:")) != -1)
{
  switch (c)
  {
    case 'v':
      verbose_flag ++;
      break;
    case 'b':
      binary_flag ++;
      break;
    case 'f':
      output_filename = optarg;
      break;
    case '?':
      printf("Unknown option %c\n", c);
      usage();
      exit(1);
  }
}

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