Win32 WndProc as class member [duplicate]

Question

Is there a way to wrap WndProc as private member?

If I have this:

class Window
{
public:
    Window();
    virtual ~Window();
    void create();

private:
    LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam);
};

And in my create() this:

WNDCLASSEX wc;
wc.lpfnWndProc = (WNDPROC) &Window::WndProc;

I get this warning:

warning: converting from 'LRESULT (Window::*)(HWND, UINT, WPARAM, LPARAM) {aka long int (Window::*)(HWND__*, unsigned int, unsigned int, long int)}' to 'WNDPROC {aka long int (__attribute__((__stdcall__)) *)(HWND__*, unsigned int, unsigned int, long int)}' [-Wpmf-conversions]

And my window HWND is NULL, GetLastError() also returns 0.

How can this be fixed?

Answer 1

You should add the static modifier to it.

The reason for this, is that when it's a member function (which I believe is a __thiscall in Visual C++), it's actually just a C function taking this as the first parameter. This would look like this:

LRESULT CALLBACK WndProc(Window& this, HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam);

If you make it static, the compiler gets rid of the first Window& this parameter, making it compatible with lpfnWndProc .

Answer 2

Make it static:

static LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam);