getsubopt(3) — Linux manual page

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | STANDARDS | HISTORY | NOTES | EXAMPLES | SEE ALSO | COLOPHON

getsubopt(3)            Library Functions Manual            getsubopt(3)

NAME         top

       getsubopt - parse suboption arguments from a string

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #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         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 │
       └─────────────────────────────────────┴───────────────┴─────────┘

STANDARDS         top

       POSIX.1-2008.

HISTORY         top

       POSIX.1-2001.

NOTES         top

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

EXAMPLES         top

       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         top

       getopt(3)

COLOPHON         top

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Linux man-pages 6.9.1          2024-06-15                   getsubopt(3)

Pages that refer to this page: getopt(3)