Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!thunder.mcrcim.mcgill.edu!snorkelwacker.mit.edu!stanford.edu!agate!spool.mu.edu!mips!cs.uoregon.edu!ogicse!milton!sumax!polari!rwing!seaeast!burklabs!ronb
From: ronb@burklabs (Ron Burk       )
Newsgroups: comp.windows.ms.programmer
Subject: Hacking The Dialog Class
Message-ID: <c5HP41w163w@burklabs>
Date: 17 Jun 91 22:10:35 GMT
Organization: Burk Labs, Redmond WA
Lines: 15

For obscure reasons, I have written a program that replaces the window
function defined in window class "#32770" (a window class defined by
USER.EXE).  In effect, this puts my own callback function in the chain
for many Windows dialog boxes.  To accomplish this, I defined and
exported a window callback function, created a dummy window of class
"#32770", did a SetClassLong to poke in the address of my callback
function (using MakeProcInstance, of course), then deleted the dummy
window.  This is fine and dandy and everything works as expected
except for one small fact:  when my callback function gets invoked,
the data segment is set correctly, but the stack segment seems to
belong to the application who put up the window (SS != DS).  I made
my application work simply by not depending on SS == DS, but
what gives?  How could my callback function get called with
my data segment and someone else's stack?  It's not a DLL, just
a simple program.