using System;  using System.Collections.Generic;  using System.ComponentModel;  using System.Data;  using System.Drawing;  using System.IO;  using System.Text;  using System.Windows.Forms;      namespace 读取host文件  {      public partial class Form1 : Form      {          public Form1()          {              InitializeComponent();          }              private void button1_Click(object sender, EventArgs e)          {              string str;              StreamReader sr = new StreamReader(@"C:\windows\system32\drivers\etc" + "\\hosts", false);              str = sr.ReadToEnd().ToString();              sr.Close();              this.richTextBox1.Text = str;///读取            }       }    }    @"C:\windows\system32\drivers\etc" + "\\hosts"文件路径