SAMPLE: KbHook.exe Demos Keyboard Hook Function Keyboard Filter

ID: Q66989

The information in this article applies to:

SUMMARY

KbHook.exe is a file in the Software Library that contains sample code to demonstrate the installation and use of a system-wide keyboard filter function (otherwise known as a keyboard hook function). This code monitors the status of the CAPS LOCK key. Whenever the CAPS LOCK key is pressed, its status is displayed on the application's icon. Terminating the application removes the keyboard filter from the system.

MORE INFORMATION

The following file is available for download from the Microsoft Software Library: 

 ~ KbHook.exe (size: 22361 bytes)
For more information about downloading files from the Microsoft Software Library, please see the following article in the Microsoft Knowledge Base: 

   ARTICLE-ID: Q119591
   TITLE     : How to Obtain Microsoft Support Files from
               Online Services
NOTE: The KbHook.exe sample uses the SetWindowsHook() function. Applications written for Windows 3.1 should use the SetWindowsHookEx() function.

KbHook.exe contains an application program, KEYAPP, and a dynamic-link library (DLL), KEYHOOK, that implements the keyboard filter function.

KEYAPP calls KEYHOOK to install the keyboard filter function and then makes itself iconic. Windows calls KEYHOOK each time a key is pressed. When the CAPS LOCK key is pressed, KEYHOOK posts a message to KEYAPP. KEYAPP processes the message by painting its icon to display the current state of CAPS LOCK. When KEYAPP is terminated, the KEYHOOK filter is removed from the system.

Because the keyboard filter function is called regardless of the application that is currently active, the code must be in memory at all times. When Windows 3.0 is running in real mode with extended memory, code for inactive applications can be placed into extended memory banks that are switched out of memory. Windows's memory management scheme is defined so that code in fixed DLLs will remain in memory at all times and will remain available for execution.

For more information on the keyboard filter function, see the documentation for the SetWindowsHook() function on pages 4-419 through 4-427 in the "Microsoft Windows Software Development Kit Reference Volume 1" for the Windows SDK version 3.0. For additional information on the SetWindowsHookEx() function see pages 896-899 of "Programmer's Reference, Volume 2: Functions" from the Windows SDK version 3.1. The "Microsoft Windows Software Development Kit Guide to Programming" provides additional information on DLLs.

Additional query words: Keywords : kbfile kbsample kb16bitonly kbHook kbGrpUser kbWinOS310 kbWinOS300

Last Reviewed: December 10, 1998