getsubopt(3p) — Linux manual page


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

       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-

       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         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 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;

               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.1‐2017, stdlib.h(0p)

COPYRIGHT         top

       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 .

       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               2017                     GETSUBOPT(3P)

Pages that refer to this page: stdlib.h(0p)