GetBorderSize

CSize GetBorderSize(const CWnd& window)
{
   if (window.IsZoomed())
   {
      // The total border size is found by subtracting the size of the client rect
      // from the size of the window rect. Note that when the window is zoomed, the
      // borders are hidden, but the title bar is not.
      CRect wndRect, clientRect;
      window.GetWindowRect(&wndRect);
      window.GetClientRect(&clientRect);
      return wndRect.Size() - clientRect.Size();
   }
   else
   {
      // Determine the border size by asking windows to calculate the window rect
      // required for a client rect with a width and height of 0. This method will
      // work before the window is fully initialized and when the window is minimized.
      CRect rect;
      AdjustWindowRectEx(&rect, window.GetStyle(), FALSE, window.GetExStyle());
      return rect.Size();
   }
}