C#从文本文件读取指定行

      C#（VS 2008）的与文件操作相关的类FileStream、StreamReader等，他们封装好的函数不够方便对文本文件制定行进行操作。但是利用StreamReader类的ReadLine可以间接地实现这个操作。实现方法有很多种，这里列举一种网上很多朋友都熟知的方法。另外，从文本文件制定位置读取可以调用API函数实现（当然也有其他方式），具体方法如有需要可以索取。

//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();

                     }

                 }

             }

         }