getsubopt - parse suboption arguments from a string


   #include <stdlib.h>

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

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

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


   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:


   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.


   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


   For  an  explanation  of  the  terms  used   in   this   section,   see

   Interface    Attribute      Value   
   getsubopt()  Thread safety  MT-Safe 


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


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


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

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

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

               case RW_OPT:
                   readwrite = 1;

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

                   name = value;

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

               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");

       /* Remainder of program... */





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