/sys$common/syshlp/helplib.hlb DCE_RPC, idl, ARGUMENTS, -caux  *Conan The Librarian (sorry for the slow response - running on an old VAX)

   -caux filename

   Specifies a pathname for the client auxiliary file. When you give a
   filename, do not give a file extension; the idl compiler appends .c
   to the C source file and .o to the object file.  If you do not use
   the -caux argument, the idl compiler appends _caux.c to the C
   source file and _caux.o to the object file. If the -lang cxx option
   is used, the source file will have the .cxx extension.