GetModuleHandle(NULL) vs hInstance

Question

When programming using the Windows API, I've always made the HINSTANCE from WinMain a global variable immediately. If I want to make an OK button, I'd do it like so (given global HINSTANCE g_hInstance):

return CreateWindow("BUTTON", "OK", WS_TABSTOP|WS_VISIBLE|WS_CHILD|BS_DEFPUSHBUTTON, 10, 10, 100, 30, exampleParentWindow, EXAMPLECHILDID, g_hInstance, NULL); 

but lately I've been seeing the instance handle determined without having to be passed as a parameter or clogging up the global namespace, using a call to GetModuleHandle(NULL)*. So, the example above would look like this:

return CreateWindow("BUTTON", "OK", WS_TABSTOP|WS_VISIBLE|WS_CHILD|BS_DEFPUSHBUTTON, 10, 10, 100, 30, exampleParentWindow, EXAMPLECHILDID, GetModuleHandle(NULL), NULL); 

*If your compiler supports it, you can write GetModuleHandle(nullptr) and the statement will have the same result.

What's the advantage (if any) of calling GetModuleHandle(NULL) over explicitly specifying the instance handle?

_{Fine Print: I know this has an answer, but it has not been phrased as its own question on StackOverflow.}

Answer 1

In an EXE, it does not make any difference. hInstance from WinMain() and GetModuleHandle(NULL) both refer to the same HINSTANCE (the module of the .exe file). But it does make a difference if you are creating windows inside of a DLL instead, since you have to use the DLL's hInstance but GetModuleHandle(NULL) will still return the HINSTANCE of the EXE that loaded the DLL.