// example struct: (sequential layout = just like C, the struct is just a memory-area with names...)
		[StructLayout(LayoutKind.Sequential)]
		struct HARDWAREINPUT
		{
			public uint uMsg;
			public ushort wParamL;
			public ushort wParamH;
		}

// example union: (explicit lets you give each field an offset, careful though, it's not as simple as it seems)
		[StructLayout(LayoutKind.Explicit, Size = 28)]
		struct INPUT
		{
			[FieldOffset(0)]
			public InputSource type;
			[FieldOffset(4)]
			public MOUSEINPUT mi;
			[FieldOffset(4)]
			public KEYBDINPUT ki;
			[FieldOffset(4)]
			public HARDWAREINPUT hi;
		}
// example, how-to-use:
		[StructLayout(LayoutKind.Sequential)]
		public struct LPRECT
		{
			public long left;
			public long top;
			public long right;
			public long bottom;
		}
		[DllImport("user32.dll")]
		public static extern bool GetClientRect(IntPtr hWnd, ref LPRECT lpRect);