I’d recommend you deal with this the way Windows Forms does it internally:
public static IntPtr GetWindowLong(HandleRef hWnd, int nIndex)
{
if (IntPtr.Size == 4)
{
return GetWindowLong32(hWnd, nIndex);
}
return GetWindowLongPtr64(hWnd, nIndex);
}
[DllImport("user32.dll", EntryPoint="GetWindowLong", CharSet=CharSet.Auto)]
private static extern IntPtr GetWindowLong32(HandleRef hWnd, int nIndex);
[DllImport("user32.dll", EntryPoint="GetWindowLongPtr", CharSet=CharSet.Auto)]
private static extern IntPtr GetWindowLongPtr64(HandleRef hWnd, int nIndex);