NAME

       getsubopt - parse suboption arguments from a string

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <stdlib.h>

       int getsubopt(char **restrict optionp, char *const *restrict tokens,
                     char **restrict 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 │
       └───────────────────────────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       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.

EXAMPLES

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

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

       #include <assert.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)