STL map常用操作简介 http://www.kuqin.com/cpluspluslib/20071231/3264.html
STL中map用法详解 http://www.kuqin.com/cpluspluslib/20071231/3265.html http://blog.sina.com.cn/s/blog_a9303fd9010195hm.html
buffer的线索 https://www.cnblogs.com/zhjh256/p/6346501.html