StreamReader与StreamWriter读写文件

             //FileStream aFile = new FileStream(@"c:\1.txt", FileMode.Open, FileAccess.ReadWrite);
            StreamReader sr = new StreamReader(@"c:\1.txt",Encoding.Default);
            string str=sr.ReadLine();
            textBox1.Text = str;
            sr.Close();

    
            //FileStream aFile = new FileStream(@"c:\1.txt", FileMode.Open, FileAccess.Write);
            StreamWriter sw = new StreamWriter(@"C:\1.txt",false,Encoding.Default);
            sw.WriteLine("yyya明天");            
            sw.Close();
            ```