NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON

GETSUBOPT(3)              Linux Programmer's Manual             GETSUBOPT(3)

NAME         top

       getsubopt - parse suboption arguments from a string

SYNOPSIS         top

       #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         top

       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         top

       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         top

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

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

CONFORMING TO         top

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

NOTES         top

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

EXAMPLE         top

       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         top

       getopt(3)

COLOPHON         top

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GNU                              2016-03-15                     GETSUBOPT(3)