Platform SDK: Interprocess Communications |
The SysMsgProc hook procedure is a library-defined callback function used with the SetWindowsHookEx function. The system calls this function 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 function can monitor messages for any dialog box, message box, menu, or scroll bar in the system.
The HOOKPROC type defines a pointer to this callback function. SysMsgProc is a placeholder for the library-defined function name.
LRESULT CALLBACK SysMsgProc( int nCode, // message flag WPARAM wParam, // not used LPARAM lParam // message data );
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. |
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.
If nCode is less than zero, the hook procedure must return the value returned by CallNextHookEx.
If nCode is greater than or equal to zero, and the hook procedure did not process the message, it is highly recommended that you call CallNextHookEx and return the value it returns; otherwise, other applications that have installed WH_SYSMSGFILTER hooks will not receive hook notifications and may behave incorrectly as a result. If the hook procedure processed the message, it may return a nonzero value to prevent the system from passing the message to the target window procedure.
An application installs the hook procedure by specifying the WH_SYSMSGFILTER hook type and a pointer to the hook procedure in a call to the SetWindowsHookEx function.
Windows NT/2000: Requires Windows NT 3.1 or later.
Windows 95/98: Requires Windows 95 or later.
Header: Declared in Winuser.h; include Windows.h.
Hooks Overview, Hook Functions, CallNextHookEx, MSG, SetWindowsHookEx