C#读写改TXT文件

Question

            string fileAbsolutePath = @"d:\x.txt"; //你的txt文件的路径            StringBuilder txtLines = new StringBuilder();
            using (StreamReader sr = new StreamReader(@fileAbsolutePath, System.Text.Encoding.Default))
            {
                while (!sr.EndOfStream)
                {
                    txtLines.AppendLine(sr.ReadLine().TrimStart('a'));
                }
                sr.Close();
            }
            using (StreamWriter sw = new StreamWriter(@fileAbsolutePath, false, System.Text.Encoding.Default))
            {
                sw.Write(txtLines.ToString());
            }