Is calling DispatchMessage in win32 programs necessary?

Question

Win32 programs generally have a message loop that loops calling GetMessage or PeekMessage, and then calls DispatchMessage to dispatch the message to the window proceedure of the relevant window.

But is there any need to actually do this? Can I instead just look in the MSG object directly in the message loop and perform the actions needed there without calling DispatchMessage? I'm talking about cases where I have one single window with no other window controls, for example if the window is only used as a direct3d display window, so messages will always be directed at the only window.

Mostly I'm just curious but also it might lead to certain aspects of my code being cleaner too.

Answer 1

You call DispatchMessage to have the message delivered to proper window, to its "window proc". You think you have one window only, but is it really the only one? COM will create helper windows, other subsystems might create helper hidden windows as well, who is going to deliver messages posted to shared message queue and addressed to those windows. Without having to think a lot about these details you have API to dispatch them. And you have to do it because those subsystems are relying on presence of message pump.

Spy++ Windows SDK tool might help you with seeing how many windows you really have.

Still if you indeed have the only window, it does not make much of a difference whether you handler is called from DispatchMessage internals, or directly by your message pump.