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

    Returns the port number on which the specified service is
    waiting.
    Format
      #include  <rpc/pmap_clnt.h>
      u_short  pmap_getport(struct sockaddr_in *addr, u_long prognum,
               u_long versnum, u_long protocol );

1 - Arguments

 addr
    A pointer to a sockaddr_in structure containing the internet
    address of the host where the remote Portmapper resides.
 prognum
    The program number associated with the remote procedure.
 versnum
    The version number associated with the remote procedure.
 protocol
    The transport protocol that the remote procedure uses. Specify
    either IPPROTO_UDP or IPPROTO_TCP.

2 - Description

    A client interface to the Portmapper. This routine returns the
    port number on which waits a server that supports program number
    prognum, version versnum, and speaks the transport protocol
    associated with protocol (IPPROTO_UDP or IPPROTO_TCP).

                                  NOTES
       If the requested version is not available, but at least the
       requested program is registered, the routine returns a port
       number.

       The pmap_getport routine returns the port number in host
       byte order not network byte order. For certain routines you
       may need to convert this value to network byte order using
       the htons routine. For example, the sockaddr_in structure
       requires that the port number be in network byte order.

3 - Return Values

    x                  The port number of the service on the remote
                       system.
    0                  No mapping exists or RPC could not contact the
                       remote Portmapper service. In the latter case,
                       the global variable rpc_createerr.cf_error
                       contains the ONC RPC status.