1     class Program
 2     {
 3         static void Main(String[] args)
 4         {
 5             //写入string数组，每个string一行
 6             string[] lines = { "first line", "second line ", "third line", "forth line" };
 7             System.IO.File.WriteAllLines(@"D:\IOTest\IOTest1.txt", lines);
 8             //写入一个字符串
 9             string text = "ahhhhhhhhhhhhhhhhhhhhhhhhhhh";
10             System.IO.File.WriteAllText(@"D:\IOTest\IOTest2.txt", text);
11             //StreamWriter类，以流的方式写入
12             System.IO.StreamWriter file = new System.IO.StreamWriter(@"D:\IOTest\IOTest3.txt", true);
13             foreach (var line in lines)
14             {
15                 if (!line.Contains("second"))
16                 {
17                     file.Write(line);
18                     file.WriteLine(line);
19                 }
20             }
21             file.Flush();
22             file.Close();
23         }
24     }

 1     class Program
 2     {
 3         static void Main(String[] args)
 4         {
 5             //读取为一个字符串
 6             string text = System.IO.File.ReadAllText(@"D:\iOTEST\IOTEST2.TXT");
 7             //读取为字符串数组，每行一个字符串
 8             string[] lines = System.IO.File.ReadAllLines(@"D:\IOTEST\IOTEST1.TXT");
 9             //StreamReader类，以流的方式读取
10             System.IO.StreamReader sr = new System.IO.StreamReader(@"D:\iOTEST\IOTEST3.TXT");
11             string str;
12             while ((str = sr.ReadLine()) != null)
13             {
14                 Console.WriteLine(str);
15             }
16             sr.Close();
17         }
18     }