将消息发送到不存在的窗口可以吗？

Question

I have a thread that send update messages to a window, I use ::SendMessage() and ::PostMessage() APIs.

I go in and out of multiple dialogs and register the dialog that I am currently in with the thread via the window handle ( m_hWnd ). If I exit all the way out, the main application window doesn't handle these messages. For that reason I don't register that window. At this point the thread will have the handle of an older window which now doesn't exist.

Is it okay if it sends messages to that non-existent window? I am assuming it should not do any harm but wanted to double check.

Answer 1

No, it is not ok to post a message to a deleted window.
There is no guarantee noone will set up shop at that address just after the previous tennant is gone.

If you use a NULL window handle, you'll post a thread message to the current threads message queue. SendMessage as far as I could google shoul be a no-op.
Might be harmless enough.

Now, we get tricky:

Under specific cicumstances it does not matter, pre-supposing well-behaved applications.

1. A message like WM_NULL should not make anything happen.
2. A window-message you globally registered in your application using RegisterWindowMessage , if you can guarantee none of your applications windows created in the meantime will choke on it.