CODEWITHSUNDEEP
c++winapi
kwjsksai
kwjsksai

Reputation: 347

hInstance in CreateWindow

I use CreateWindow to create the main window. hInstance in WNDCLASSEX specifies the instance under which the class is registered. So I need hInstance in CreateWindow function to find it.

I use CreateWindow to create a button. No user-defined WNDCLASSEX now. The BUTTON's WNDCLASSEX is global. But I still need to pass an hInstance to the function? Why and what is the right value to pass?

In Microsoft's example it's (HINSTANCE)GetWindowLong(hMainWnd, GWL_HINSTANCE), but I have no idea of what it is.

Please also tell me if I had anything wrong.

Thanks.

Upvotes: 5

Views: 20120

Answers (3)

Bence Szebedy
Bence Szebedy

Reputation: 596

When you create a window, you specify the class of which an instance is created with a string (lpClassName) in the first parameter of CreateWindow.

hInstance is used for identification in case more than one DLL referenced contains a class with the same name.

For more information see https://devblogs.microsoft.com/oldnewthing/20050418-59/?p=35873

Upvotes: 3

Eric Juaneda
Eric Juaneda

Reputation: 51

I found in MSDN dated from 2001 for CreateWindow and CreateWindowEx

hInstance

Windows 95/98/Me: [in] Handle to the instance of the module to be associated with the window.

Windows NT/2000/XP: This value is ignored.

Upvotes: 5

Qaz
Qaz

Reputation: 61970

But I still need to pass an hInstance to the function? Why and what is the right value to pass?

As for the why, it would be a bit pointless (at least from a winapi perspective) to make a whole new function that takes everything but that and just uses the parent's or something when all other parameters still have a use.

I personally don't know for sure what the right value to pass in is, but I use GetModuleHandle(nullptr), which should be equivalent to the instance passed into WinMain. It would also be the same as the one Microsoft's example uses (which gets the instance used to create the parent window) if that's what you use to create the parent window. The difference would come in if using a different application's window as the parent. The other main option I see used is nullptr/NULL, which has worked the same way as the aforementioned options every time I have used it.

If there's a subtle difference today between using NULL and the application's HINSTANCE, I'd like to know, but either of those should work fine for creating child controls on your windows.

Upvotes: 2

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