Excerpted from message dated 03-06-97, Mike Phillips to Jonathan de
  Boyne Pollard (original subject "The (highly unofficial) F"):

MP>OS/2 Warp Control Program API
  >Author: Marc Stock
  >Publisher: John Wiley & Sons, Inc.
  >ISBN: 0-471-03887-3
  >Copyright date: 1995

MP>This is a good book for programmers new to OS/2 and have never dealt
  >with interprocess communication or extended attributes before...  It
  >also covers the undocumented DosSelToFlat() and DosFlatToSel()
  >functions.

Hi Mike--

    DosSelToFlat() and DosFlatToSel() are documented on page 3-17 of the
OS/2 2.0 Technical Library manual "Application Design Guide" (IBM p/n
10G6260).  The easiest way to find the documentation (unless you are a
packrat and still have those "obsolete" version 2.0 manuals) is by using
the "DevCon Browser" in DevCon volume 12 (December 1996).  A search on
DosSelToFlat will lead you directly to the right place in the CD-ROM
on-line version of that manual.

    Perhaps the reason later IBM OS/2 Control-Program manuals do not
document DosSelToFlat (and its reverse) is that they are not used with
"modern" (since 1993) compilers designed specifically for OS/2 2.0 and
later.  The IBM C/C++ Tools compiler (v 2) uses the _Seg16 type
qualifier to declare pointers used in both 16-bit and 32-bit portions of
the code ("C/C++ Tools Programming Guide," March 1993 edition, p 289)
and the compiler takes care of the thunking.  I use PL/I for OS/2 for
writing text-mode programs, and the necessary thunking API calls are
handled by that compiler, automatically.  I have not used any other
compilers with OS/2 since the ill-designed (and poorly implemented)
Borland BCOS2 v 1.0, so cannot speak for them.

   Regards, 

          --Murray

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