SAMPLE: Code Demonstrates Using a WH_KEYBOARD Hook

The information in this article applies to:

• Microsoft Windows Software Development Kit (SDK) for Windows version 3.1

SUMMARY

KBHOOK2 is a file in the Software Library that contains sample code to demonstrate installing and using a system-wide WH_KEYBOARD 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.

KBHOOK2 updates the KBHOOK sample to use new functions provided by Windows 3.1. For more information on the KBHOOK sample, query on the following words in the Microsoft Knowledge Base:

   kbhook

• Microsoft Download Service (MSDL)

        Dial (206) 936-6735 to connect to MSDL
        Download KBHOOK2.EXE (size: 26280 bytes) 
  

• Internet (anonymous FTP)

        ftp ftp.microsoft.com
        Change to the \SOFTLIB\MSLFILES directory
        Get KBHOOK2.EXE (size: 26280 bytes) 
  

MORE INFORMATION

KBHOOK2 contains an application program, KEYAPP, and a dynamic-link library (DLL), KEYHOOK, that implements the keyboard filter function. The KEYHOOK DLL uses the new Windows 3.1 hook functions: SetWindowsHookEx, UnhookWindowsHookEx, and CallNextHookEx.

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.

NOTE: Compiling this sample as is will fail with the error that the include file CONVDLL.INC cannot be found. To correct the problem, simply remove the line

   INCLUDE CONVDLL.INC