The WM_DESTROY message is sent when a window is being destroyed. It is sent to the window procedure of the window being destroyed after the window is removed from the screen.
This message is sent first to the window being destroyed and then to the child windows (if any) as they are destroyed. During the processing of the message, it can be assumed that all child windows still exist.
WM_DESTROY
This message has no parameters.
If an application processes this message, it should return zero.
If the window being destroyed is part of the clipboard viewer chain (set by calling the SetClipboardViewer function), the window must remove itself from the chain by processing the ChangeClipboardChain function before returning from the WM_DESTROY message.
ChangeClipboardChain, DestroyWindow, PostQuitMessage, SetClipboardViewer, WM_CLOSE