C# Definition:

    [ComImport(),
    InterfaceType(ComInterfaceType.InterfaceIsIUnknown),
    GuidAttribute("000214e4-0000-0000-c000-000000000046")]
    public    interface IContextMenu
    {
        // IContextMenu methods
        [PreserveSig()]
        int    QueryContextMenu(uint hmenu, uint iMenu, int idCmdFirst, int idCmdLast, uint uFlags);
        [PreserveSig()]
        void    InvokeCommand (IntPtr pici);
        [PreserveSig()]
        void    GetCommandString(int idcmd, uint uflags, int reserved,            
        IntPtr commandstring, int cch);
    }

        private void MemCopy(IntPtr source, IntPtr dest, int cch)
        {
            byte[] buff = new byte[cch];
            Marshal.Copy(source, buff, 0, cch);
            Marshal.Copy(buff, 0, dest, cch);
        }

        private void WriteStringToPtrUnicode(IntPtr dest, string str, int cch)
        {
            IntPtr tempStrPtr = Marshal.StringToCoTaskMemUni(str);
            MemCopy(tempStrPtr, dest, cch);
            Marshal.FreeHGlobal(tempStrPtr);
        }

public void GetCommandString(int idcmd, uint uflags, int reserved, IntPtr commandstring, int cch)

        {    
            if (uflags == (uint)GCS.HELPTEXTW)

            {
                switch(idcmd)
                {
                    case 0:

                        WriteStringToPtrUnicode(commandstring, "My help string", cch);
                        break;