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From: "Sylvan W. Clebsch" <sylvan@NOSPAMstanford.edu>
Newsgroups: comp.os.ms-windows.programmer.win32
Subject: Re: Subclassing WndProc in another process
Date: Wed, 6 Aug 1997 13:46:07 -0700
Organization: Stanford University
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>I create a systemwide hook with SetWindowsHookEx, but the hook function
>is never called (at least not in NT).

a couple of things about system wide hooks:

1) they have to be in a DLL in order to work
2) remember you have to supply the library handle OR the module handle, and
a thread ID of 0

my personal approach to hooks is to place them in a DLL along with their
"startup" functions. that why i can link directly to the DLL in my app and
not LoadLibrary on it. i call the "startup" function from my app, which
internally calls something like:

 HHOOK hHook = SetWindowsHookEx(
    WH_CBT,
// the type of hook
    (HOOKPROC)HookProc,
// the filter function
    (HMODULE)GetModuleHandle( "DLLNAME.DLL" ),        // DLL module handle
    NULL
// zero to install it system wide
    );

note that if you put a breakpoint on it, you will only break when it is
called from your app, not when its called from the rest of the system. also,
for system wide hooks don't forget to make sure any global data you need to
be shared system wide is placed in a shard data segment. you will need to do
the following:

#pragma data_seg( ".SHARDATA" )
int    someSharedInt
#pragme data_seq()

that goes right in your source module. in addition, you will need a .def
file (normally not needed for a 32bit DLL since you can just use
__declspec(dllexport), but now you need one, heheh). add this to your module
definition file:

SECTIONS
    .SHARDATA      Read Write Shared

that should do it. i hope this helps.

-s