The WM_CLOSE message is sent as a signal that a window or an application should terminate.
WM_CLOSE
Parameters
This message has no parameters.
Return Values
If an application processes this message, it should return zero.
Default Action
The DefWindowProc function calls the DestroyWindow function to destroy the window.
Remarks
An application can prompt the user for confirmation, prior to destroying a window, by processing the WM_CLOSE message and calling the DestroyWindow function only if the user confirms the choice.
See Also