class WriteTextFile     {         static void Main()         {             //如果文件不存在，则创建；存在则覆盖             //该方法写入字符数组换行显示             string[] lines = { "first line", "second line", "third line","第四行" };             System.IO.File.WriteAllLines(@"C:\testDir\test.txt", lines, Encoding.UTF8);             //如果文件不存在，则创建；存在则覆盖             string strTest = "该例子测试一个字符串写入文本文件。";             System.IO.File.WriteAllText(@"C:\testDir\test1.txt", strTest, Encoding.UTF8);             //在将文本写入文件前，处理文本行             //StreamWriter一个参数默认覆盖             //StreamWriter第二个参数为false覆盖现有文件，为true则把文本追加到文件末尾             using (System.IO.StreamWriter file = new System.IO.StreamWriter(@"C:\testDir\test2.txt",true))             {                 foreach (string line in lines)                 {                     if (!line.Contains("second"))                     {                         file.Write(line);//直接追加文件末尾，不换行                         file.WriteLine(line);// 直接追加文件末尾，换行                       }                 }             }         }     }

class ReadTextFile     {         static void Main()         {             //直接读取出字符串             string text = System.IO.File.ReadAllText(@"C:\testDir\test1.txt");             Console.WriteLine(text);             //按行读取为字符串数组             string[] lines = System.IO.File.ReadAllLines(@"C:\testDir\test.txt");             foreach (string line in lines)             {                 Console.WriteLine(line);             }             //从头到尾以流的方式读出文本文件             //该方法会一行一行读出文本             using (System.IO.StreamReader sr = new System.IO.StreamReader(@"C:\testDir\test.txt"))             {                 string str;                 while ((str = sr.ReadLine()) != null)                 {                     Console.WriteLine(str);                 }             }             Console.Read();         }     }