More Subclassing...

Following my previous thread about SubClassing, I have another question:

Since Subclassing using SetWindowLong API is limited to windows in your own thread, I tried to think about ways to Subclass other windows:

When I SetWindowLong with the new address of the proccess, I assume what it does is change the value of the address in the memory.
Is it possible to Subclass othwer windows using CopyMemory in any way?

I'd appreciate any reply.

Thanks.

Ok this isnt my thread, but I would be interested in seeing the answer.....

[Yonatan]

It would be possible, but there's no way to actually know the address of the GWL_WNDPROC variable, and that is necessary for changing it...
However, you can use hooks!
Try the WH_JOURNALRECORD hook.
It's one of the only two hooks which you can use in VB in system-wide mode without creating any VC++ DLL.
This hook passes you every message that happens to any hWnd currently in existance - limited to window handles in your own RAM.
However, you cannot tell the hook to discard the message or to replace it with your own... You can only view it and add code in VB. (Well, it's NOT a Subclass...)
In the MSDN and the Platform SDK, look up: SetWindowsHookEx (<== or just click there)

[Sam Finch]

in fact the problem with subclassing other processes in VB isn't the GWL_WNDPROC variable. The problem is the address of your substitute process.


I'm not sure if my terminoligy is correct for 32 bit windows, but I'd assume these names havn't changed since windows 3.x


All the Data you can access using Get/Set window long is stored in one area of memory, called the BurgerMaster (named after a restaraunt where Bill and his pals used to hang out while working on Windows 1.0)

the hWnd of a window is its address in the BurgerMaster, get.set Window long take an offset from this address to the address of the variable you want (they're all -ve, the hWnd is the address of the next free bit of memory after the window data) This can be accessed from any process.


When the window recieves a message it looks at the value of its GWL_WNDPROC variable and looks at that memory address in the process that the window is associated with, this memory address contains something called a thunk.

a thunk is a bit of machine code that calls your code for you, it is used to set up the chip registers and page tables and copy parameters to the right bits of memory.

so when the window gets the message it calls this thunk.

If you set the GWL_WNDPROC variable to the address of a thunk in your own process the window still looks in its process for the thunk, but the address its given only contains a valid thunk in your process, in its process it could contain anything. So it crashes.

A while ago I experimented with playing around a bit with these thunks, and I found you could use copymemory to copy the thunk from the address given by the addressof operator of a function into a byte array, and you could still subclass using the address of the byte array instead of the address of the procedure.

My next step was going to be to attempt to copy the thunk file of my process into another process using virtualallocex and write process memory, then set the GWL_WNDPROC variable to the address I copied it to, making sure I didn't use any variables in my window procedure, instead making the area of memory I allocated big enough to hold any data I needed and using read/write ProccessMemory to get/set these variables.

Needless to say I decided not to do this and to learn C++ instead.

but If you wnat to try that feel free.

Wow! That sounds a little complicated
I hope that in the future VB will be able to create standard DLLs.
But the WH_JOURNALRECORD sounds interesting.

How do you do this smiley that looks up?

:rolleyes:

cool.
do you have some other codes for other faces?

big grin
confused
cool
eek!
embarrasment
frown
mad
roll eyes (sarcastic)
smile
stick out tongue
wink

here is how you use them


:D big grin
:confused: confused
:cool: cool
:eek: eek!
:o embarrasment
:( frown
:mad: mad
:rolleyes: roll eyes (sarcastic)
:) smile
:p stick out tongue
;) wink

thanks denniswrenn