LRESULT SendMessage( HWND hWnd,
UINT Msg,
WPARAM wParam,
LPARAM lParam
);
hWnd
[in] Handle to the window whose window procedure will receive the message. If this parameter is HWND_BROADCAST, the message is sent to all top-level windows in the system, including disabled or invisible unowned windows, overlapped windows, and pop-up windows; but the message is not sent to child windows.
Msg
[in] Specifies the message to be sent.
wParam
[in] Specifies additional message-specific information.
lParam
[in] Specifies additional message-specific information.