Example of Getopt (The GNU C Library) (original) (raw)

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 fromgetopt. 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 -