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GETSUBOPT(3)               Linux Programmer's Manual              GETSUBOPT(3)
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 sub-
       option.  The value extends to the next comma, or (for the  last  subop-
       tion) 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  get-
       subopt()  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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GNU                               2017-09-15                      GETSUBOPT(3)