流（Stream）与文件流（FileStream）

            //通过流的方式添加
            StreamWriter writer = new StreamWriter(@"C:\A\ca.txt", true, Encoding.Default);
            writer.WriteLine("早上好");
            writer.WriteLine("中午好");
            writer.Close();

            //通过流的当时读取
            StreamReader reader = new StreamReader(@"C:\A\ca.txt", Encoding.Default);
            Console.WriteLine(reader.ReadToEnd());
            while (reader.Peek() > 0)
            {
                Console.WriteLine(reader.ReadLine());
            }
            reader.Close();

文件流（FileStream）

            //文件流添加
            byte[] arr = Encoding.Default.GetBytes("你好");   
            FileStream fsw = new FileStream(@"C:\A\ca.txt", FileMode.Create);      
            fsw.Write(arr, 0, arr.Length);
            fsw.Close();
            //文件流读取
            byte[] arr1 = new byte[200];
            FileStream fsr = new FileStream(@"C:\A\c.txt", FileMode.Open);
            fsr.Read(arr1, 0, 200);
            fsr.Close();
            Console.WriteLine(Encoding.Default.GetString(arr1));