Is there an equivalent function in WinAPI to GLFW's glfwGetWindowUserPointer?

Question

So I've created a window using WinAPI and I have a WindowProc callback function that handles window messages. In this function I want to access my own struct that wraps around the WinAPI HWND, to change other variables stored in this struct.

I know that GLFW supplies the functions glfwSetWindowUserPointer and glfwGetWindowUserPointer to fill this need. I tried searching for GetWindowUserPointer, WindowUserPointer, WindowPointer and UserPointer on https://learn.microsoft.com/en-us/windows/desktop, but found no results.

Is there any function or otherwise method to fill this need using WinAPI?

Answer 1

There is SetWindowLongPtr() and GetWindowLongPtr()

The window creator always may use GWLP_USERDATA, you can store any data pointer of your choice. If you reserve additional space (cbWndExtra) when registering the window class, you can store additional data at positive offsets as well.

A common technique is to use WM_NCCREATE to copy a pointer from the lpParam parameter of CreateWindowEx and copy it to the window data using SetWindowLongPtr. Then other cases in the window procedure can retrieve the pointer and get your associated object.

Raymond Chen has a complete explanation of using this feature to forward messages to a member function.