http://blog.csdn.net/zephyr_be_brave/article/details/8944967
http://www.cnblogs.com/yunsicai/p/3326105.html
http://www.cppblog.com/prayer/archive/2009/08/17/93597.html
http://www.jianshu.com/p/41ad81a5d504
原文：http://www.cnblogs.com/yxzfscg/p/4758668.html