C# FileStream复制大文件功能

public static class FileHelper
  {
    /// <summary>
    /// 复制大文件
    /// </summary>
    /// <param name="fromPath">源文件的路径</param>
    /// <param name="toPath">文件保存的路径</param>
    /// <param name="eachReadLength">每次读取的长度</param>
    /// <returns>是否复制成功</returns>
    public static bool CopyFile(string fromPath, string toPath, int eachReadLength)
    {
      //将源文件 读取成文件流
      FileStream fromFile = new FileStream(fromPath, FileMode.Open, FileAccess.Read);
      //已追加的方式 写入文件流
      FileStream toFile = new FileStream(toPath, FileMode.Append, FileAccess.Write);
      //实际读取的文件长度
      int toCopyLength = 0;
      //如果每次读取的长度小于 源文件的长度 分段读取
      if (eachReadLength < fromFile.Length)
      {
        byte[] buffer = new byte[eachReadLength];
        long copied = 0;
        while (copied <= fromFile.Length - eachReadLength)
        {
          toCopyLength = fromFile.Read(buffer, 0, eachReadLength);
          fromFile.Flush();
          toFile.Write(buffer, 0, eachReadLength);
          toFile.Flush();
          //流的当前位置
          toFile.Position = fromFile.Position;
          copied += toCopyLength;
        }
        int left = (int)(fromFile.Length - copied);
        toCopyLength = fromFile.Read(buffer, 0, left);
        fromFile.Flush();
        toFile.Write(buffer, 0, left);
        toFile.Flush();
 
      }
      else
      {
        //如果每次拷贝的文件长度大于源文件的长度 则将实际文件长度直接拷贝
        byte[] buffer = new byte[fromFile.Length];
        fromFile.Read(buffer, 0, buffer.Length);
        fromFile.Flush();
        toFile.Write(buffer, 0, buffer.Length);
        toFile.Flush();
 
      }
      fromFile.Close();
      toFile.Close();
      return true;
    }
  }

class Program
  {
    static void Main(string[] args)
    {
 
      Stopwatch watch = new Stopwatch();
      watch.Start();
      if (FileHelper.CopyFile(@"D:\安装文件\新建文件夹\SQLSVRENT_2008R2_CHS.iso", @"F:\SQLSVRENT_2008R2_CHS.iso", 1024 * 1024 * 5))
      {
        watch.Stop();
        Console.WriteLine("拷贝完成,耗时：" + watch.Elapsed.Seconds + "秒");
      }
      Console.Read();
    }
  }