using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;
//compile with /unsafe
 
namespace CopyDataInterop
{
    public partial class Form1 : Form
    {
        public const int WM_COPYDATA = 0x004a;
 
        [StructLayout(LayoutKind.Sequential)]
        public struct COPYDATASTRUCT
        {
            [MarshalAs(UnmanagedType.I4)]
            public int dwData;
            [MarshalAs(UnmanagedType.I4)]
            public int cbData;
            [MarshalAs(UnmanagedType.SysInt)]
            public IntPtr lpData;
        }
 
        public Form1()
        {
            InitializeComponent();
            this.Text = "HWND " + this.Handle.ToString();
        }
 
        unsafe protected override void WndProc(ref Message message)
        {
            if (message.Msg == WM_COPYDATA)
            {
                COPYDATASTRUCT data = (COPYDATASTRUCT)
                    message.GetLParam(typeof(COPYDATASTRUCT));
 
                string str = new string((char*)(data.lpData), 
                    0, data.cbData/2);
 
                MessageBox.Show(str, "Data received", 
                    MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
            }
            base.WndProc(ref message);
        }
 
        unsafe private void SendString()
        {
            string s = this.textBox2.Text;
            IntPtr lpData = Marshal.StringToHGlobalUni(s);
 
            COPYDATASTRUCT data = new COPYDATASTRUCT();
            data.dwData = 0;
            data.cbData = s.Length * 2;
            data.lpData = lpData;
 
            IntPtr lpStruct = Marshal.AllocHGlobal(
                Marshal.SizeOf(data));
 
            Marshal.StructureToPtr(data, lpStruct, false);
 
            int hTarget = Convert.ToInt32(textBox1.Text);
 
            SendMessage(hTarget, WM_COPYDATA, 
                this.Handle, lpStruct);
        }
 
        private void button1_Click(object sender, EventArgs e)
        {
            SendString();
        }
 
        [DllImport("User32.dll")]
        private static extern bool SendMessage(int hWnd,
            int wMsg, IntPtr wParam, IntPtr lParam);
 
    }
}