How should Error Status Code returned from a DLLImport function be handled?

        //Output：    None
        //return：    0 - success, <0 - failure(refer to error code definition)
        //Note：        None
        [DllImport("./libraries/something.dll", CallingConvention = CallingConvention.Cdecl)]
        public static extern int OpenDevice(int nPort, int nBaud);

        //Output：    None
        //return：    0 - success, <0 - failure(refer to error code definition)
        //Note：        None
        [DllImport("./libraries/something.dll", CallingConvention = CallingConvention.Cdecl)]
        public static extern int OpenDevice(int nPort, int nBaud);