DOCUMENT:Q66989 23-JUL-2001 [win16sdk] TITLE :KbHook.exe Demos Keyboard Hook Function Keyboard Filter PRODUCT :Microsoft Windows Software Development Kit PROD/VER::3.0,3.1 OPER/SYS: KEYWORDS:kbfile kbsample kbHook kbGrpDSUser kbOSWin310 kbOSWin300 kb16bitonly ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Windows Software Development Kit (SDK) versions 3.0, 3.1 ------------------------------------------------------------------------------- SUMMARY ======= KbHook.exe is a file in the Microsoft Download Center 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 Download Center: KbHook.exe For additional information about how to download Microsoft Support files, click the article number below to view the article in the Microsoft Knowledge Base: Q119591 How to Obtain Microsoft Support Files from Online Services Microsoft used the most current virus detection software available on the date of posting to scan this file for viruses. Once posted, the file is housed on secure servers that prevent any unauthorized changes to the file. 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 kbHook kbGrpDSUser kbOSWin310 kbOSWin300 kb16bitonly Technology : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK300 kbWinSDK310 Version : :3.0,3.1 ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2001.