http://www.eefocus.com/andysun001/blog/10-07/192341_cd0c0.html
http://topic.csdn.net/u/20090417/13/6169972c-390e-427b-bd05-119afb937f1b.html
http://loveolive.com/courses/CLang/dir/se1203.htm
fread读到EOF的时候就终止了，不会继续读取了，也不回会读取EOF
