IPC between .NET and C++ applications

Question

Are there any libraries for inter-process communication (IPC) between a .NET application and a native C++ application?

Answer 1

A simple (though limited) IPC mechanism is the WM_COPYDATA message

You can easily use it to transmit a struct to a native application.

I use the following helper class :

public static class CopyDataHelper
{

    [StructLayout(LayoutKind.Sequential)]
    public struct COPYDATASTRUCT
    {
        private int _dwData;
        private int _cbData;
        private IntPtr _lpData;

        public int DataId
        {
            get { return _dwData; }
            set { _dwData = value; }
        }

        public int DataSize
        {
            get { return _cbData; }
        }

        public IntPtr Data
        {
            get { return _lpData; }
        }

        public void SetData(T data) where T : struct
        {
            int size = Marshal.SizeOf(typeof(T));
            IntPtr ptr = Marshal.AllocHGlobal(size);
            Marshal.StructureToPtr(data, ptr, true);
            _lpData = ptr;
            _cbData = size;
        }

        public T GetData() where T : struct
        {
            return (T)Marshal.PtrToStructure(_lpData, typeof(T));
        }
    }

    [DllImport("User32.dll")]
    private static extern bool SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, ref COPYDATASTRUCT lParam);

    public const int WM_COPYDATA = 0x004A;

    public static bool Send(IntPtr fromHwnd, IntPtr toHwnd, int dataId, T data) where T : struct
    {
        IntPtr ptr = IntPtr.Zero;
        try
        {
            COPYDATASTRUCT cds = new COPYDATASTRUCT();
            cds.DataId = dataId;
            cds.SetData(data);
            return SendMessage(toHwnd, WM_COPYDATA, fromHwnd, ref cds);
        }
        finally
        {
            if (ptr != IntPtr.Zero)
                Marshal.FreeHGlobal(ptr);
        }
    }

    public static COPYDATASTRUCT Receive(Message msg)
    {
        if (msg.Msg != WM_COPYDATA)
            throw new ArgumentException("This is not a WM_COPYDATA message");
        COPYDATASTRUCT cds = (COPYDATASTRUCT)msg.GetLParam(typeof(COPYDATASTRUCT));
        return cds;
    }

}

To catch the WM_COPYDATA message, you need to override WndProc :

    protected override void WndProc(ref Message msg)
    {
        if (msg.Msg == CopyDataHelper.WM_COPYDATA)
        {
            CopyDataHelper.COPYDATASTRUCT cds = CopyDataHelper.Receive(msg);
            if (cds.DataId == myDataId)
            {
                MyData data = cds.GetData();
                msg.Result = DoSomething(data);
                return;
            }
        }

        base.WndProc(ref msg);
    }