c#对文件的操作

//创建文件
public static void WriteFile(string str)
         {
             StreamWriter sr;           
             if (File.Exists(FILE_NAME)) //如果文件存在,则创建File.AppendText对象
             {
                 sr = File.AppendText(FILE_NAME);
             }
             else   //如果文件不存在,则创建File.CreateText对象
             {
                 sr = File.CreateText(FILE_NAME);
             }
             sr.WriteLine(str);
             sr.Close();
         }

用C#读取文本文件中指定的行

//用ArrayList必须加这句；
using System.Collections;
//读文件；
//path 工作目录； fgf 分隔符；
public ArrayList readTxtFile(string path,string fgf)
         {
             if (!File.Exists(path))
             {
                 Console.WriteLine("文件不存在！");
                 Console.WriteLine("按回车键退出！");
                 Console.ReadLine();
                 return null;
             }                
             try
             {
                 //读出一行文本，并临时存放在ArrayList中
                 StreamReader sr = new StreamReader(path, Encoding.GetEncoding("gb2312"));
                 string l;
                 ArrayList content = new ArrayList();
                 while((l = sr.ReadLine()) != null)
                 {
                     ArrayList row = new ArrayList();
                     l = l.Trim();
                     int length = l.Length;
                     int i = 0;
                     bool fgf_flag = false;
                     while(i < length)
                     {
                         string x = l[i].ToString();
                         i++;
                         if (x.Equals(fgf))
                         {
                             fgf_flag = true;
                             row.Add(l.Substring(0,i-1));
                             length = length-i+1;
                             i = 0;
                         }    
                     }
                     if (!fgf_flag)
                         row.Add(l);
                     row.TrimToSize();

                     //将多行文本储存在ArrayList中，并返回；
                     content.Add(row);
                 }
                 sr.Close();
                 content.TrimToSize();
                 return content;
             }
             catch(IOException ex)
             {
                 Console.WriteLine("读文件出错！请检查文件是否正确。");
                 Console.WriteLine(ex.ToString());
                 return null;
             }
         }

//写文件；
public void writeTxtFile(string path,string fgf,ArrayList a)
         {
             //保存文件已存在
             if (File.Exists(path))
             {
                 Console.WriteLine("文件已存在！是否覆盖（O）、追加（A）该文件？退出直接按回车键。");
                 string over_flag = Console.ReadLine().ToString().Trim();
                
                 //追加到文件末尾
                 if (over_flag.Equals("A")||over_flag.Equals("a"))
                 {
                     try
                     {
                         StreamWriter sw = new StreamWriter(path,true,Encoding.GetEncoding("gb2312"));
                         IEnumerator cIE = a.GetEnumerator();
                         while (cIE.MoveNext())
                         {
                             ArrayList row =(ArrayList)cIE.Current;

                             //读取文本行中的字符段，并输出文件
                             IEnumerator rIE = row.GetEnumerator();
                             int length = row.Count;
                             int i = 0;
                             while (rIE.MoveNext())
                             {
                                 string st = rIE.Current.ToString();
                                 if (i==length-1)
                                     sw.Write(st);
                                 else
                                     sw.Write(st+fgf);
                                 i++;
                             }
                             sw.WriteLine();
                         }
                         sw.Close();
                         Console.WriteLine("写文件完毕，按回车键退出。。。");
                         Console.ReadLine();
                     }
                     catch(IOException ex)
                     {
                         Console.WriteLine(ex.ToString());
                         Console.WriteLine("写文件出错！请检查文件是否正确。按回车键退出。。。");
                         Console.ReadLine();
                     }
                 }
             }
            
         }
     }
}