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From: lwallace@javelin.sim.es.com (Raptor)
Newsgroups: comp.windows.ms.programmer
Subject: Passing data to a DLL; strange problem!
Message-ID: <1991Apr22.173022.8930@javelin.sim.es.com>
Date: 22 Apr 91 17:30:22 GMT
Organization: Evans & Sutherland Computer Corp., Salt Lake City, Utah
Lines: 56

(One wonders if I'll ever find a Windows technique that works the
first time I try it...)

I've recently broken my application up into a DLL and a main program
module.  One of the functions I've exported to the DLL needs to
enumerate top-level windows, so I want to pass it my application's
top-level window handle to feed FindWindow().

First, if you've got a better technique to do this, I'm interested in
hearing it.  But my problem remains.

I've written a tiny function to pass the handle to a static variable
in the DLL.  This is what's in the DLL:

HWND ParentHandle;
...
void FAR PASCAL TxferParentHandle(HWND hwnd)
{
ParentHandle = hwnd;
}

This is how I call it from my main module:

HWND ParentHandle;
...
WinMain(...)
{
...
TxferParentHandle(hwnd);
}

The DLL's copy of ParentHandle remains 0.  hwnd is set as expected.
It was baffling to execute the assignment statement in CodeView and
see that it doesn't work!

I have discovered, through CodeView, that the address of ParentHandle
in the DLL is in a different segment from that shown in DS and SS
(which are equal):

(for example)
&ParentHandle = 0c15:2794
DS = 0bea
SS = 0bea

This is in my DLL, just after TxferParentHandle() is called.  The
assembly code uses the correct offset (2794 in this case).  It's just
going to a different segment, for some reason.

Both modules are compiled (and linked) with the small model.

Has anyone encountered this?  Any suggestions?
-- 
            Lynn Wallace           |           I do not represent E&S.
Evans and Sutherland Computer Corp.|   Internet: lwallace@javelin.sim.es.com
      Salt Lake City, UT 84108     |           Compu$erve:  70242,101
	      Revenge is a dish best not served at all.