private void button2_Click(object sender, EventArgs e)
    {
      using (FileStream fsWrite = new FileStream(@"D:\1.txt", FileMode.Append))
      {
        string temp = "";
        for (int i = 0; i < 10000;i++ )
        {
          temp += i.ToString()+"/t";

        }
        byte [] m = System.Text.Encoding.UTF8.GetBytes (temp);
        fsWrite.Write(m, 0, temp.Length);
      }
    }

private void Readtxt()
{
  using (FileStream fsRead = new FileStream(@"d:\2.txt,FileMode.Open"))
  {
    //剩余文件內(nèi)容長(zhǎng)度
    long leftLength = fsRead.Length;
    //buffersize 
    int buffersize = 1024;
    //創(chuàng)建緩存數(shù)組
    byte[] buffer = new byte[buffersize];
    int rNum = 0;
    int FileStart = 0;
    while(leftLength > 0)
    {
      //設(shè)置文件流的讀取位置
      fsRead.Position = FileStart ;
      if (leftLength < buffersize)
      {
        rNum = fsRead.Read(buffer, 0, Convert.ToInt32(leftLength));
      }
      else
        {
          rNum = fsRead.Read(buffer, 0, maxLength);
        }
        if (rNum == 0)
        {
          break;
        }
        fileStart += rNum;
        leftLength -= rNum;
        //字節(jié)轉(zhuǎn)換
         string msg = System.Text.Encoding.UTF8.GetString(buffer);//

        byte[] myByte = System.Text.Encoding.UTF8.GetBytes(msg);//
         //寫(xiě)入文件
        using (FileStream fsWrite = new FileStream(@"d:\2.txt, FileMode.Append))//處理完成再追加
        {
          fsWrite.Write(myByte, 0, myByte.Length);
        }
    }
    fsRead.Close();
  }
}