C# FileStream复制大文件

/// <summary>/// 复制文件/// </summary>/// <param name="fromFile">要复制的文件</param>/// <param name="toFile">要保存的位置</param> /// <param name="lengthEachTime">每次复制的长度</param>    private void CopyFile(string fromFile, string toFile, int lengthEachTime)    {      FileStream fileToCopy = new FileStream(fromFile, FileMode.Open, FileAccess.Read);      FileStream copyToFile = new FileStream(toFile, FileMode.Append, FileAccess.Write);      int lengthToCopy;      if (lengthEachTime < fileToCopy.Length)//如果分段拷贝，即每次拷贝内容小于文件总长度      {        byte[] buffer = new byte[lengthEachTime];        int copied = 0;        while (copied <= ((int)fileToCopy.Length - lengthEachTime))//拷贝主体部分        {          lengthToCopy = fileToCopy.Read(buffer, 0, lengthEachTime);          fileToCopy.Flush();          copyToFile.Write(buffer, 0, lengthEachTime);          copyToFile.Flush();          copyToFile.Position = fileToCopy.Position;          copied += lengthToCopy;        }        int left = (int)fileToCopy.Length - copied;//拷贝剩余部分        lengthToCopy = fileToCopy.Read(buffer, 0, left);        fileToCopy.Flush();        copyToFile.Write(buffer, 0, left);        copyToFile.Flush();      }      else//如果整体拷贝，即每次拷贝内容大于文件总长度      {        byte[] buffer = new byte[fileToCopy.Length];        fileToCopy.Read(buffer,0,(int)fileToCopy.Length);        fileToCopy.Flush();        copyToFile.Write(buffer, 0, (int)fileToCopy.Length);        copyToFile.Flush();      }      fileToCopy.Close();      copyToFile.Close();    }