把文件流读入字节数组的几种方法

OpenFileDialog ofd = new OpenFileDialog();
if (ofd.ShowDialog() == DialogResult.OK)
fullfilename = ofd.FileName.ToString();//获取文件完整路径
FileStream fs = new FileStream(fullfilename, FileMode.Open, FileAccess.Read);

//把文件流读入字节数组，方法一：
int filelength = (int)fs.Seek(0, SeekOrigin.End);//获取文件流长度
fs.Seek(0, SeekOrigin.Begin);//？？？
byte[] buff = new byte[filelength];
////把文件流读入字节数组，方法二：
byte[] buff = new byte[fs.Length];
////把文件流读入字节数组，方法三：
//BinaryReader br = new BinaryReader(fs);
//int filelength = (int)fs.Length;//获取文件流长度
//byte[] buff = br.ReadBytes((int)fs.Length);

fs.Read(buff, 0, (int)filelength);
//fs.Read(buff, 0, (int)fs.Length);
fs.Close();