25.3.13 Parsing of Suboptions Example

The code which might appear in the mount(8) program is a perfect example of the use of getsubopt:

     #include <stdio.h>
     #include <stdlib.h>
     #include <unistd.h>
     
     int do_all;
     const char *type;
     int read_size;
     int write_size;
     int read_only;
     
     enum
     {
       RO_OPTION = 0,
       RW_OPTION,
       READ_SIZE_OPTION,
       WRITE_SIZE_OPTION,
       THE_END
     };
     
     const char *mount_opts[] =
     {
       [RO_OPTION] = "ro",
       [RW_OPTION] = "rw",
       [READ_SIZE_OPTION] = "rsize",
       [WRITE_SIZE_OPTION] = "wsize",
       [THE_END] = NULL
     };
     
     int
     main (int argc, char *argv[])
     {
       char *subopts, *value;
       int opt;
     
       while ((opt = getopt (argc, argv, "at:o:")) != -1)
         switch (opt)
           {
           case 'a':
             do_all = 1;
             break;
           case 't':
             type = optarg;
             break;
           case 'o':
             subopts = optarg;
             while (*subopts != '\0')
               switch (getsubopt (&subopts, mount_opts, &value))
                 {
                 case RO_OPTION:
                   read_only = 1;
                   break;
                 case RW_OPTION:
                   read_only = 0;
                   break;
                 case READ_SIZE_OPTION:
                   if (value == NULL)
                     abort ();
                   read_size = atoi (value);
                   break;
                 case WRITE_SIZE_OPTION:
                   if (value == NULL)
                     abort ();
                   write_size = atoi (value);
                   break;
                 default:
                   /* Unknown suboption. */
                   printf ("Unknown suboption `%s'\n", value);
                   break;
                 }
             break;
           default:
             abort ();
           }
     
       /* Do the real work. */
     
       return 0;
     }