Best method for storing this pointer for use in WndProc

Question

I\'m interested to know the best / common way of storing a this pointer for use in the WndProc. I know of several approaches, but each as I underst

Answer 1

In the past I've used the lpParam parameter of CreateWindowEx:

lpParam [in, optional] Type: LPVOID

Pointer to a value to be passed to the window through the CREATESTRUCT structure (lpCreateParams member) pointed to by the lParam param of the WM_CREATE message. This message is sent to the created window by this function before it returns. If an application calls CreateWindow to create a MDI client window, lpParam should point to a CLIENTCREATESTRUCT structure. If an MDI client window calls CreateWindow to create an MDI child window, lpParam should point to a MDICREATESTRUCT structure. lpParam may be NULL if no additional data is needed.

The trick here is to have a static std::map of HWND to class instance pointers. Its possible that the std::map::find might be more performant than the SetWindowLongPtr method. Its certainly easier to write test code using this method though.

Btw if you are using a win32 dialog then you'll need to use the DialogBoxParam function.