[plt-scheme] FFI and pointer manipulations

Hi all,

With the FFi how do I add an integer to a c-pointer?

More specifically I am interested in getting a pointer
into the middle of a byte-string.

 From my last question, I know that byte-strings are
c-pointers:

   > (cpointer? (bytes 0 1))
   #t

I couldn't find anything on pointer arithmetic besides
ptr-equal? in the FFI manual.

-- 
Jens Axel Søgaard