using (FileStream fs = new FileStream(txtFilePathRead.Text, FileMode.Open))
                {
                   byte[] arr = new byte[1024 * 1024 * 2];
                   fs.Read(arr, 0, arr.Length);                  

                   string strContent = System.Text.Encoding.Default.GetString(arr);
                   txtReadContent.Text = strContent;                                 

                 }

 byte[] arr = new byte[1024 * 1024 * 2];
                   fs.Read(arr, 0, arr.Length);        Read方法返回类型是int类型，是什么意义啊，不太理解这里 read是每次读arr.length 还是一次性的读完 ，谁能帮忙说说这三个参数分别什么意思吗？谢了