C# Definition:

[StructLayout(LayoutKind.Sequential)]
struct COPYDATASTRUCT
{
    public IntPtr dwData;
    public int cbData;
    public IntPtr lpData;
}

const int WM_COPYDATA = 0x004A;

VB.NET Definition:

<StructLayout(LayoutKind.Sequential)> _
Structure COPYDATASTRUCT
   Public dwData As IntPtr
   Public cdData As Integer
   Public lpData As IntPtr
End Structure

User-Defined Field Types:

None.