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

 xdrs
    A pointer to the XDR stream handle being created. The routine
    xdrstdio_create fills in xdrs with encoding and decoding
    information..
 file
    A pointer to the FILE structure that is to be associated with the
    stream.
 op
    An XDR operation, one of: XDR_ENCODE, XDR_DECODE, and XDR_FREE.