enum usb_relay_device_type
	{
		USB_RELAY_DEVICE_ONE_CHANNEL = 1,
		USB_RELAY_DEVICE_TWO_CHANNEL = 2,
		USB_RELAY_DEVICE_FOUR_CHANNEL = 4,
		USB_RELAY_DEVICE_EIGHT_CHANNEL = 8	
	};
	struct usb_relay_device_info
	{
		unsigned char *serial_number;
		char *device_path;
		usb_relay_device_type type;
		usb_relay_device_info* next;
	};

	int __declspec(dllexport) usb_relay_init(void);

	struct usb_relay_device_info __declspec(dllexport) * usb_relay_device_enumerate(void);

	void __declspec(dllexport) usb_relay_device_free_enumerate(struct usb_relay_device_info*);

	int __declspec(dllexport) usb_relay_device_open_with_serial_number(const char *serial_number, unsigned len);

	int __declspec(dllexport)  usb_relay_device_open(struct usb_relay_device_info* device_info);

	int __declspec(dllexport) usb_relay_device_get_status(int hHandle, unsigned int *status);

	int __declspec(dllexport) usb_relay_device_set_serial(int hHandle, char serial[5]);

public class USBRelayDevice
    {
        const string _dllLocation = "usb_relay_device.dll";

        public enum usb_relay_device_type
        {
            USB_RELAY_DEVICE_ONE_CHANNEL = 1,
            USB_RELAY_DEVICE_TWO_CHANNEL = 2,
            USB_RELAY_DEVICE_FOUR_CHANNEL = 4,
            USB_RELAY_DEVICE_EIGHT_CHANNEL = 8
        }

        public unsafe struct usb_relay_device_info
        {
            public string serial_number;
            public IntPtr device_path;
            public usb_relay_device_type type;
            public IntPtr next_usb_relay_device_info;
        };

        [DllImport(_dllLocation, CallingConvention=CallingConvention.Cdecl)]
        public static extern int usb_relay_init();

        [DllImport(_dllLocation, CallingConvention=CallingConvention.Cdecl)]
        public static extern void usb_relay_device_free_enumerate(ref usb_relay_device_info strct);

        [DllImport(_dllLocation, CallingConvention=CallingConvention.Cdecl)]
        public static extern int usb_relay_device_open_with_serial_number(IntPtr serial_number, uint len);

        [DllImport(_dllLocation, CallingConvention=CallingConvention.Cdecl)]
        public static extern int  usb_relay_device_open(ref usb_relay_device_info device_info);

        [DllImport(_dllLocation, CallingConvention=CallingConvention.Cdecl)]
        public static extern int usb_relay_device_get_status(int hHandle, IntPtr status);

    }

int __declspec(dllexport) usb_relay_device_set_serial(int hHandle, char serial[5]);
struct usb_relay_device_info __declspec(dllexport) * usb_relay_device_enumerate(void);