文件流

如果文件太大就不能全部读入到内存中，需要建立一个缓冲区来一点一点的读取文件。

using(FileStream outStream = new FileStream(@"D:\kankan\b.xv",FileMode.Create))//建立保存文件流
            {
                byte[] lengths = new byte[1024];//缓冲区大小
                int realylength;//真实读取大小
                using (FileStream inStream = new FileStream(@"D:\kankan\a.xv", FileMode.Open))//建立读取文件流
                {
                    while((realylength=inStream.Read(lengths,0,lengths.Length))>0)//有可能读到某一时刻读取的内容没有缓冲区那么多
                    {
                        outStream.Write(lengths, 0, realylength);
                    }
                }
            }