VMS Help TCPIP Services, Programming Interfaces, RPC XDR Routines, xdr_pointer, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    An XDR routine for translating data structures that contain
    pointers to other structures, such as a linked list. The xdr_
    pointer routine is similar to the xdr_reference routine. The
    differences are that the xdr_pointer routine handles pointers
    with the value NULL and that it translates the pointer values to
    a boolean. If the boolean is TRUE, the data follows the boolean.