Searching a user space

I have an xml document loaded into a user space and I want to find a specific 
tag.  I can use the %Scan BIF but I'm looking for something that will search 
the entire user space at one time without having to loop and check 64k at a 
time.

Currently I'm trying to use the C strstr function but it keeps giving me a 
pointer value when the search string doesn't exist in the user space.  I have 
listed the associated code below.

If anyone sees a problem with my code or has a better way I'm all ears (or eyes 
in this case).

      // Search for substring                                                   
                 
     d SchStr          pr              *   ExtProc('strstr')                    
Error number     
     d                                 *   Const Options(*String)               
String to search 
     d                                 *   Const Options(*String)               
String to find   

      // XML string being worked on                            
     d XMLString@      s               *                       
     d XMLString       s          64000    Based(XMLString@)   
                                                               

     d TmpPtr          s               * 

      // Search constants                                
     d b_PDF           s              5    Inz('<pdf ')  

         TmpPtr = SchStr(%TrimR(XMLString) :b_PDF); 

Rick