  Opening an RMS file twice? (sharing) 
 The Question is:
 
Is there a way of intermingling RMS and UNIX
I/O routines on the same file? More specifically, if I open a file using the
UNIX I/O open command, is there any way I can
retrieve the FAB that the emulation library is
using?
 
 The Answer is:
 
  While the underlying RMS FAB structure is accessable via the "acc"
  access callback that is available on the open and creat calls, your
  proposed approach would involve shared access on the same channel and
  the OpenVMS Wizard strongly recommends against this -- you could very
  easily confuse the C library's view of the file.
 
  You can quite easily and simply open the RMS file twice, if the first
  access to the file permits compatible sharing.  If using the creat or
  open call, specify the "shr" file sharing keyword, and specify the file
  access that other channels are permitted to request.
 
  In particular, please see the OpenVMS FAQ section that describes how
  to open a file for shared access -- that section will also point you
  back to topic 2867 here in the Ask The Wizard area for an example.
 
