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CallMsgFilter info  Overview  Group

The CallMsgFilter function passes the specified message and hook code to the hook procedures associated with the WH_SYSMSGFILTER and WH_MSGFILTER hooks. A WH_SYSMSGFILTER or WH_MSGFILTER hook procedure is an application-defined callback function that examines and, optionally, modifies messages for a dialog box, message box, menu, or scroll bar.

BOOL CallMsgFilter(

    LPMSG lpMsg,

// pointer to structure with message data

    int nCode 

// hook code



Pointer to an MSG structure that contains the message to be passed to the hook procedures.
Specifies an application-defined code used by the hook procedure to determine how to process the message. The code must not have the same value as system-defined hook codes (MSGF_ and HC_) associated with the WH_SYSMSGFILTER and WH_MSGFILTER hooks.

Return Values

If the application should process the message further, the return value is zero.

If the application should not process the message further, the return value is nonzero.


Windows calls CallMsgFilter to enable applications to examine and control the flow of messages during internal processing of dialog boxes, message boxes, menus, and scroll bars, or when the user activates a different window by pressing the ALT+TAB key combination.

An application installs a hook procedure by using the SetWindowsHookEx function.

See Also

MessageProc, MSG, SetWindowsHookEx, SysMsgProc

file: /Techref/os/win/api/win32/func/src/f03_23.htm, 2KB, , updated: 2000/4/7 12:19, local time: 2022/5/26 01:45,

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