NAME

       getsubopt - parse suboption arguments from a string

SYNOPSIS

       #include <stdlib.h>

       int getsubopt(char **optionp, char * const *tokens, char **valuep);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       getsubopt():
           _XOPEN_SOURCE >= 500
               || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L

DESCRIPTION

       getsubopt() parses the list of comma-separated suboptions provided in optionp.  (Such a suboption list is
       typically produced when getopt(3) is used to parse a command line; see  for  example  the  -o  option  of
       mount(8).)  Each suboption may include an associated value, which is separated from the suboption name by
       an equal sign.  The following is an example of the kind of string that might be passed in optionp:

           ro,name=xyz

       The tokens argument is a pointer to a NULL-terminated array of pointers to the  tokens  that  getsubopt()
       will look for in optionp.  The tokens should be distinct, null-terminated strings containing at least one
       character, with no embedded equal signs or commas.

       Each call to getsubopt() returns information about the next unprocessed suboption in optionp.  The  first
       equal  sign  in a suboption (if any) is interpreted as a separator between the name and the value of that
       suboption.  The value extends to the next comma, or (for the last suboption) to the end  of  the  string.
       If  the name of the suboption matches a known name from tokens, and a value string was found, getsubopt()
       sets *valuep to the address of that string.  The first comma in optionp is overwritten with a null  byte,
       so *valuep is precisely the "value string" for that suboption.

       If the suboption is recognized, but no value string was found, *valuep is set to NULL.

       When  getsubopt() returns, optionp points to the next suboption, or to the null byte ('\0') at the end of
       the string if the last suboption was just processed.

RETURN VALUE

       If the first suboption in optionp is recognized, getsubopt() returns the index of the matching  suboption
       element in tokens.  Otherwise, -1 is returned and *valuep is the entire name[=value] string.

       Since  *optionp  is  changed, the first suboption before the call to getsubopt() is not (necessarily) the
       same as the first suboption after getsubopt().

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌────────────┬───────────────┬─────────┐
       │Interface   │ Attribute     │ Value   │
       ├────────────┼───────────────┼─────────┤
       │getsubopt() │ Thread safety │ MT-Safe │
       └────────────┴───────────────┴─────────┘

CONFORMING TO

       POSIX.1-2001, POSIX.1-2008.

NOTES

       Since getsubopt() overwrites any commas it finds in the string *optionp, that string must be writable; it
       cannot be a string constant.

EXAMPLE

       The following program expects suboptions following a "-o" option.

       #define _XOPEN_SOURCE 500
       #include <stdlib.h>
       #include <assert.h>
       #include <stdio.h>

       int
       main(int argc, char **argv)
       {
           enum {
               RO_OPT = 0,
               RW_OPT,
               NAME_OPT
           };
           char *const token[] = {
               [RO_OPT]   = "ro",
               [RW_OPT]   = "rw",
               [NAME_OPT] = "name",
               NULL
           };
           char *subopts;
           char *value;
           int opt;

           int readonly = 0;
           int readwrite = 0;
           char *name = NULL;
           int errfnd = 0;

           while ((opt = getopt(argc, argv, "o:")) != -1) {
               switch (opt) {
               case 'o':
                   subopts = optarg;
                   while (*subopts != '\0' && !errfnd) {

                   switch (getsubopt(&subopts, token, &value)) {
                   case RO_OPT:
                       readonly = 1;
                       break;

                   case RW_OPT:
                       readwrite = 1;
                       break;

                   case NAME_OPT:
                       if (value == NULL) {
                           fprintf(stderr, "Missing value for "
                                   "suboption '%s'\n", token[NAME_OPT]);
                           errfnd = 1;
                           continue;
                       }

                       name = value;
                       break;

                   default:
                       fprintf(stderr, "No match found "
                               "for token: /%s/\n", value);
                       errfnd = 1;
                       break;
                   }
               }
               if (readwrite && readonly) {
                   fprintf(stderr, "Only one of '%s' and '%s' can be "
                           "specified\n", token[RO_OPT], token[RW_OPT]);
                   errfnd = 1;
               }
               break;

               default:
                   errfnd = 1;
               }
           }

           if (errfnd || argc == 1) {
               fprintf(stderr, "\nUsage: %s -o <suboptstring>\n", argv[0]);
               fprintf(stderr, "suboptions are 'ro', 'rw', "
                       "and 'name=<value>'\n");
               exit(EXIT_FAILURE);
           }

           /* Remainder of program... */

           exit(EXIT_SUCCESS);
       }

SEE ALSO

       getopt(3)

COLOPHON

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