Manpages - getsubopt.3

getsubopt - parse suboption arguments from a string

  #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

*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.

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*().

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

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>

  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);
  }

*getopt*(3)

This page is part of release 5.13 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.