Registering Window Class

Question

I guess my question is relatively easy for those of you who spent time dealing with Win32 API.

So my question is:
After initializing a WNDCLASSEX instance we need to "register" it using the "RegisterClassEx" function, why? Why do we do that? What's the meaning of this registration and in what cases I need to register things?

Answer 1

The ATOM returned by RegisterClassEx uniquely identifies your "window class" which can then be referred to in other windows APIs. [MSDN]

Effectively it is a hash so as to reduce the amount of data processed each time a window is created or looked for. It does also mean that multiple windows with same features can be easily created and identified.

I was addressing the practical reasons above. Hans Passant's answer correctly explains this is the OO class concept provided for C. Further MSDN example.