怎样用SendMessage发送汉字字符串

///

/// 定义结构体
///

public struct COPYDATASTRUCT
{
public IntPtr dwData; //可以是任意值
public int cbData; //指定lpData内存区域的字节数
[MarshalAs(UnmanagedType.LPStr)]
public string lpData; //发送给目录窗口所在进程的数据
}

发送方：
[DllImport("User32.dll", EntryPoint = "SendMessage")]
private static extern int SendMessage(int hWnd, int Msg, int wParam, ref COPYDATASTRUCT lParam);

[DllImport("User32.dll", EntryPoint = "FindWindow")]
private static extern int FindWindow(string lpClassName, string lpWindowName);

const int WM_COPYDATA = 0x004A;//必须是这个数值，不能更改

private void btnSend_Click(object sender, EventArgs e)
{
int hWnd = FindWindow(null, @"消息接受者");
if (hWnd == 0)
{
MessageBox.Show("未找到消息接受者！");
}
else
{
string sendString = "测试发送数据";
byte[] sarr = System.Text.Encoding.Default.GetBytes(sendString);
int len = sarr.Length;
COPYDATASTRUCT cds;
cds.dwData = (IntPtr)0 ;
cds.cbData = len + 1;
cds.lpData = sendString;
SendMessage(hWnd, WM_COPYDATA, 0, ref cds);
}
}

接受方：
private static int WMA_InterPro = 0x004A;
protected override void DefWndProc(ref Message m)
{

if (m.Msg == WMA_InterPro)
{
COPYDATASTRUCT cds = new COPYDATASTRUCT();
Type t = cds.GetType();
cds = (COPYDATASTRUCT)m.GetLParam(t);
string receiveInfo=cds.lpData;
}
else
{
base.DefWndProc(ref m);
}
}