GETSUBOPT(3)               POSIX Programmer's Manual              GETSUBOPT(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NAME
       getsubopt -- parse suboption arguments from a string

SYNOPSIS
       #include <stdlib.h>

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

DESCRIPTION
       The getsubopt() function shall parse suboption arguments in a flag
       argument. Such options often result from the use of getopt().

       The getsubopt() argument optionp is a pointer to a pointer to the
       option argument string. The suboption arguments shall be separated by
       <comma> characters and each may consist of either a single token, or a
       token-value pair separated by an <equals-sign>.

       The keylistp argument shall be a pointer to a vector of strings. The
       end of the vector is identified by a null pointer. Each entry in the
       vector is one of the possible tokens that might be found in *optionp.
       Since <comma> characters delimit suboption arguments in optionp, they
       should not appear in any of the strings pointed to by keylistp.
       Similarly, because an <equals-sign> separates a token from its value,
       the application should not include an <equals-sign> in any of the
       strings pointed to by keylistp.  The getsubopt() function shall not
       modify the keylistp vector.

       The valuep argument is the address of a value string pointer.

       If a <comma> appears in optionp, it shall be interpreted as a suboption
       separator. After <comma> characters have been processed, if there are
       one or more <equals-sign> characters in a suboption string, the first
       <equals-sign> in any suboption string shall be interpreted as a
       separator between a token and a value. Subsequent <equals-sign>
       characters in a suboption string shall be interpreted as part of the
       value.

       If the string at *optionp contains only one suboption argument
       (equivalently, no <comma> characters), getsubopt() shall update
       *optionp to point to the null character at the end of the string.
       Otherwise, it shall isolate the suboption argument by replacing the
       <comma> separator with a null character, and shall update *optionp to
       point to the start of the next suboption argument. If the suboption
       argument has an associated value (equivalently, contains an <equals-
       sign>), getsubopt() shall update *valuep to point to the value's first
       character.  Otherwise, it shall set *valuep to a null pointer. The
       calling application may use this information to determine whether the
       presence or absence of a value for the suboption is an error.

       Additionally, when getsubopt() fails to match the suboption argument
       with a token in the keylistp array, the calling application should
       decide if this is an error, or if the unrecognized option should be
       processed in another way.

RETURN VALUE
       The getsubopt() function shall return the index of the matched token
       string, or -1 if no token strings were matched.

ERRORS
       No errors are defined.

       The following sections are informative.

EXAMPLES
   Parsing Suboptions
       The following example uses the getsubopt() function to parse a value
       argument in the optarg external variable returned by a call to
       getopt().


           #include <stdio.h>
           #include <stdlib.h>
           #include <unistd.h>

           int do_all;
           const char *type;
           int read_size;
           int write_size;
           int read_only;

           enum
           {
               RO_OPTION = 0,
               RW_OPTION,
               READ_SIZE_OPTION,
               WRITE_SIZE_OPTION
           };

           const char *mount_opts[] =
           {
               [RO_OPTION] = "ro",
               [RW_OPTION] = "rw",
               [READ_SIZE_OPTION] = "rsize",
               [WRITE_SIZE_OPTION] = "wsize",
               NULL
           };

           int
           main(int argc, char *argv[])
           {
               char *subopts, *value;
               int opt;

               while ((opt = getopt(argc, argv, "at:o:")) != -1)
                   switch(opt)
                       {
                       case 'a':
                           do_all = 1;
                           break;
                       case 't':
                           type = optarg;
                           break;
                       case 'o':
                           subopts = optarg;
                           while (*subopts != ' ')
                           {
                               char *saved = subopts;
                               switch(getsubopt(&subopts, (char **)mount_opts,
                                   &value))
                               {
                               case RO_OPTION:
                                   read_only = 1;
                                   break;
                               case RW_OPTION:
                                   read_only = 0;
                                   break;
                               case READ_SIZE_OPTION:
                                   if (value == NULL)
                                       abort();
                                   read_size = atoi(value);
                                   break;
                               case WRITE_SIZE_OPTION:
                                   if (value == NULL)
                                       abort();
                                   write_size = atoi(value);
                                   break;
                               default:
                                   /* Unknown suboption. */
                                   printf("Unknown suboption `%s'\n", saved);
                                   abort();
                               }
                           }
                           break;
                       default:
                           abort();
                       }

               /* Do the real work. */

               return 0;
           }

       If the above example is invoked with:


           program -o ro,rsize=512

       then after option parsing, the variable do__all will be 0, type will be
       a null pointer, read__size will be 512, write__size will be 0, and
       read__only will be 1. If it is invoked with:


           program -o oops

       it will print:


           "Unknown suboption `oops'"

       before aborting.

APPLICATION USAGE
       The value of *valuep when getsubopt() returns -1 is unspecified.
       Historical implementations provide various incompatible extensions to
       allow an application to access the suboption text that was not found in
       the keylistp array.

RATIONALE
       The keylistp argument of getsubopt() is typed as char ** const ** to
       match historical practice. However, the standard is clear that
       implementations will not modify either the array or the strings
       contained in the array, as if the argument had been typed const char **
       const **.

FUTURE DIRECTIONS
       None.

SEE ALSO
       getopt()

       The Base Definitions volume of POSIX.1-2017, <stdlib.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  In the event of any discrepancy between this version and the
       original IEEE and The Open Group Standard, the original IEEE and The
       Open Group Standard is the referee document. The original Standard can
       be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                         GETSUBOPT(3)
