c#读写txt文件

//write txtStringBuilder builder = new StringBuilder();FileStream fs = new FileStream(saveFileName, FileMode.Create);StreamWriter sw = new StreamWriter(fs, Encoding.Default);for (int i = 0; i < ds.Tables[0].Rows.Count; i++){        DataRow dr = ds.Tables[0].Rows[i];    builder.AppendLine(dr["netsn"] + "," + dr["imei"]); //产品S/N号 + IMEI号}sw.Write(builder);sw.Close();fs.Close();if (System.IO.File.Exists(saveFileName)){    System.Diagnostics.Process.Start(saveFileName); //保存成功后打开此文件}//read txtstring[] allLines = File.ReadAllLines(filePath);