HOOK – A HowTo for setting system wide hooks

Click this link for a Screen Shot.

Environment: MSVC++6.0 SP3, Win98/2000/NT4(SP5)

Code Description


This article features a HowTo to write, set and make use of system wide hooks.


To set system wide hooks, you need to reference a DLL in the
SetWindowsHookEx()-command. The demonstrational workspace constists of
two separate projects. One builds the DLL with its exported member functions
SetHook() and RemoveHook().

Note, that we make use of a memory mapped file to save the instance-, hook-
and window-handles which is wrapped in the struct SCGLOBALDATA.

The HookProc()-callback function is called from the system, when keycodes are
recieved. We then pass the values in lParam, wParam (virtual keycode and
keystroke-message information) via a WM_COPYDATA-message to a controlling
(separate) executable that determines by its return value if the hook is
to be forwarded through CallNextHookEx().

For additional information, the controlling procedure displays various
information on the keystroke it has currently processed. Due to the system
wide character of the hook, it even logs keys that are pressed in other
applications or a DOS-Prompt.

Member functions:

The DLL exports BOOL SetHook(HWND hWnd) and BOOL RemoveHook()
which are pretty self-explaining.
You need to pass a valid HWND to SetHook which limits the functionality to
window-applications. To bypass this, you can create a dialogbox-based
application with an initially hidden window.


Download the precompiled executable to get an idea of what hooks are all
about. The complete VC++6.0 workspace contains all necessary sourcecode
to build the demo application for you to play around with.

Final word:

I hope, you find the supplied code useful and instructive.
Please feel free to send comments to [email protected]


HookDemoExe.zip is a compiled executable of the demo application.
HookDemo.zip is a MSVC++ V6 workspace of the demo application.

Download demo project executable HookDemoExe.zip – 19.990 kBytes

Download demo project workspace HookDemo.zip – 18.120 kBytes

More by Author

Must Read