GetWindowLong loses data of fields - c++

Question

I do a wrapper for Window and want to call window methods from WndProc.
For this I pass 'this' pointer to CreateWindwEx function.
In WndProc I assign hWnd field of Window class and store it by SetWindowLongPtr
But when I try to read it by GetWindowLong I get broken instance of the window (all the fields have undefined values), however I can call w->foo()
static LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
switch (message)
{
case WM_NCCREATE:
{
LPCREATESTRUCT lpcs = reinterpret_cast<LPCREATESTRUCT>(lParam);
Window* self = static_cast<Window*>(lpcs->lpCreateParams);
// self->m_hInst and self->m_szWindowClass are set properly
// lets set hWnd
self->m_hWnd = hWnd;
SetWindowLongPtr(hWnd, GWLP_USERDATA, reinterpret_cast<LPARAM>(self));
return true;
}
case WM_COMMAND:
{
Window* w = reinterpret_cast<Window*>(GetWindowLong(hWnd, GWLP_USERDATA));
// got all the windows fields broken, though 'w' pointer itself is valid
w->foo();
int wmId = LOWORD(wParam);
// Parse the menu selections:
switch (wmId)
{
case IDM_ABOUT:
//DialogBox(m_hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About);
break;
case IDM_EXIT:
DestroyWindow(hWnd);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
}
break;
case WM_PAINT:
{
Window* w = reinterpret_cast<Window*>(GetWindowLong(hWnd, GWLP_USERDATA));
w->foo();
PAINTSTRUCT ps;
HDC hdc = BeginPaint(hWnd, &ps);
// TODO: Add any drawing code that uses hdc here...
EndPaint(hWnd, &ps);
}
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
return 0;
}
void foo()
{
//auto d = m_hInst;
auto s = m_hWnd;
}

Answer 1

My fault!
GetWindowLongPtr should be used instead of GetWindowLong