public static class Printer {

        [DllImport("ThermalServiceLibrary.dll", EntryPoint = "Port_Open", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
        public static extern int OpenPort(StringBuilder port, long speed);

        [DllImport("ThermalServiceLibrary.dll", EntryPoint = "Port_SetBaudRate")]
        public static extern int SetBaudRate(long rate);

        [DllImport("ThermalServiceLibrary.dll", EntryPoint = "Port_Close")]
        public static extern void ClosePort();

    }