WM_USER vs WM_APP

Question

I want the worker threads to send a user-defined message to the UI thread message queue, but I am not sure if I should use WM_USER or WM_APP. The d

Answer 1

If you completely control the window class of the destination window (i.e. you defined it, you're not subclassing/superclassing another class, and you don't use IsDialogMessage on your window) then you can use WM_USER+xxx (with x >= 0).

Otherwise, you should use at least WM_APP+xxx, provided you control the application that contains the window.

Failing that, the only option left would be RegisterWindowMessage().