C#P/Invoke结构问题

[DllImport("user32.dll")]
public static extern int MessageBox(IntPtr hWnd, String text, String caption, int type);

[DllImport("kernel32.dll", CharSet=CharSet.Auto)]
public static extern IntPtr GetModuleHandle(string lpModuleName);

[StructLayout(LayoutKind.Sequential)]
public struct POINT 
{
    public int X;
    public int Y;
}

[DllImport("user32.dll")]
public static extern bool GetCursorPos(out POINT lpPoint);

public delegate bool EnumWindowsProc(IntPtr hWnd, IntPtr lParam);

[DllImport("user32.dll")]
public static extern bool EnumWindows(EnumWindowsProc lpEnumFunc, IntPtr lParam);