#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())