#include<unordered_map>
一、count
mymap ['a']=101;
mymap ['c']=202;
mymap ['f']=303;
mymap.count('c');
二、find()
std::map mymap;
std::map::iterator it;
mymap['a']=50;
mymap['b']=100;
it = mymap.find('b');
if(it != mymap.end()) mymap.erase (it);
cout <<"a => "<< mymap.find('a')->second <<'\n'
三、size()
mymap.size()
四、erase()
mymap["China"] = "beijing"
mymap.erase(mymap.begin())
mymap.erase("China")
mymap.erase(mymap.find("China"), mymap.end())
