GNU Info

(libc.info)Suboptions

---

Next: Suboptions Example Prev: Argp Up: Parsing Program Arguments

---

Enter node , (file) or (file)node

Parsing of Suboptions
.....................

   Having a single level of options is sometimes not enough.  There
might be too many options which have to be available or a set of
options is closely related.

   For this case some programs use suboptions.  One of the most
prominent programs is certainly `mount'(8).  The `-o' option take one
argument which itself is a comma separated list of options.  To ease the
programming of code like this the function `getsubopt' is available.

 - Function: int getsubopt (char **OPTIONP, const char* const *TOKENS,
          char **VALUEP)
     The OPTIONP parameter must be a pointer to a variable containing
     the address of the string to process.  When the function returns
     the reference is updated to point to the next suboption or to the
     terminating `\0' character if there is no more suboption available.

     The TOKENS parameter references an array of strings containing the
     known suboptions.  All strings must be `\0' terminated and to mark
     the end a null pointer must be stored.  When `getsubopt' finds a
     possible legal suboption it compares it with all strings available
     in the TOKENS array and returns the index in the string as the
     indicator.

     In case the suboption has an associated value introduced by a `='
     character, a pointer to the value is returned in VALUEP.  The
     string is `\0' terminated.  If no argument is available VALUEP is
     set to the null pointer.  By doing this the caller can check
     whether a necessary value is given or whether no unexpected value
     is present.

     In case the next suboption in the string is not mentioned in the
     TOKENS array the starting address of the suboption including a
     possible value is returned in VALUEP and the return value of the
     function is `-1'.