SysMsgProc

The SysMsgProc hook procedure is a library-defined callback function the system calls after an input event occurs in a dialog box, message box, menu, or scroll bar, but before the message generated by the input event is processed. The hook procedure can monitor messages for any dialog box, message box, menu, or scroll bar in the system.

LRESULT CALLBACK SysMsgProc(

int nCode,	// message flag
WPARAM wParam,	// undefined
LPARAM lParam	// address of structure with message data
);

Parameters

nCode

Specifies the type of input event that generated the message. This parameter can be one of the following values:

Value	Meaning
MSGF_DIALOGBOX	The input event occurred in a message box or dialog box.
MSGF_MENU	The input event occurred in a menu.
MSGF_SCROLLBAR	The input event occurred in a scroll bar.
MSGF_NEXTWINDOW	The input event occurred as a result of the user's pressing the ALT+TAB key combination to activate a different window.

If nCode is less than zero, the hook procedure must pass the message to the CallNextHookEx function without further processing and should return the value returned by CallNextHookEx.

wParam

Specifies a NULL value.

lParam

Points to an MSG message structure.

Return Values

If the hook procedure processes the message, the return value must be nonzero. Otherwise, it must be zero.

Remarks

An application installs the hook procedure by specifying the WH_SYSMSGFILTER hook type and the address of the hook procedure in a call to the SetWindowsHookEx function.

SysMsgProc is a placeholder for the library-defined function name.

See Also

CallNextHookEx, MSG, SetWindowsHookEx

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