VMS Help CC, Messages, BADPTRARITH  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 Message        <Context> performing pointer arithmetic on a pointer
                to void or a pointer to function is not allowed.  The
                compiler will treat the type as if it were pointer to
                char.

 Description    Pointer arithmetic is not allowed on pointers to
                function or void types For compatibility with some
                other compilers, an output file is still created.
                The result produced will be the same as if the
                pointer were a pointer to char.  This may or may not
                be compatible with other compilers that accept this
                syntax.

 User Action    Cast the pointer type to a pointer to object type
                before performing the arithmetic.