strsep interface

Help, can anyone lead me in the right direction.

I tried using the below C Function incapsulated in an ile Service Pgm. When
I debug the call to the function strsep, the paramter delimiter has the
delimiter(s)  I passed but the stringp Parm always starts off as NULLand the
function promptly ends as the code says to. I don't Understand what the
prototype in Rpg must be for this function to work properly. I thought the
interface was identical to Strtok(). What does **stringp mean??

This is the prototype I am using. Its works for Strtok but not Strsep.

 d StrSep          PR             *   ExtProc('strsep')
 d  String@                          *   Value Options(*string)
 d  Delimiters@                  *   Value Options(*string)

TIA
Wayne Achenbaum
Slomins Inc.

1 /* 2  * Copyright (C) 2001  Roy Keene
 3  *
 4  * This program is free software; you can redistribute it and/or
 5  * modify it under the terms of the GNU General Public License
 6  * as published by the Free Software Foundation; either version 2
 7  * of the License, or (at your option) any later version.
 8  *
 9  * This program is distributed in the hope that it will be useful,
10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12  * GNU General Public License for more details.
13  *
14  * You should have received a copy of the GNU General Public License
15  * along with this program; if not, write to the Free Software
16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307,
USA.
17  *
18  *      email: dact@xxxxxxxxxx
19  */
20
21 /* Compliments of Jay Freeman <saurik@xxxxxxxxxx> */
22
23 #include <string.h>
24
25 char *strsep(char **stringp, const char *delim) {
26     char *ret = *stringp;
27     if (ret == NULL) return(NULL); /* grrr */
28     if ((*stringp = strpbrk(*stringp, delim)) != NULL) {
29         *((*stringp)++) = '\0';
30     }
31     return(ret);
32 }