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

PROLOG         top

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

NAME         top

       getsubopt — parse suboption arguments from a string

SYNOPSIS         top

       #include <stdlib.h>

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

DESCRIPTION         top

       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

       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         top

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

ERRORS         top

       No errors are defined.

       The following sections are informative.

EXAMPLES         top

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

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

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

               RO_OPTION = 0,

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

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

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

               /* 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.


       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         top

       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 *.



SEE ALSO         top


       The Base Definitions volume of POSIX.1‐2008, stdlib.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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 .

       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 .

IEEE/The Open Group                 2013                       GETSUBOPT(3P)