What's the logical difference between PostQuitMessage() and DestroyWindow()?

Question

In my demo kinda app

case WM_CLOSE:
    DestroyWindow(hndl);
    return 0;

and

case WM_CLOSE:
    PostQuitMessage(0);
    r         


        

Answer 1

DestroyWindow destroys the window (surprise) and posts a WM_DESTROY (you'll also get a WM_NCDESTROY) to the message queue. This is the default behaviour of WM_CLOSE. However, just because a window was destroyed does not mean the message loop should end. This can be the case for having a specific window that ends the application when closed and others that do nothing to the application when closed (e.g., an options page).

PostQuitMessage posts a WM_QUIT to the message queue, often causing the message loop to end. For example, GetMessage will return 0 when it pulls a WM_QUIT out. This would usually be called in the WM_DESTROY handler for your main window. This is not default behaviour; you have to do it yourself.