C++ primer 第十章

#include<iostream>
#include<map>
#include<set>
#include<string>
using namespace std;

typedef pair<int,string> Auth;

int main()
{
 map<int,string> m;
 set<string> s;

 Auth p1,p2,p3,p4;
 p1 = make_pair(1,"s");
 p2 = make_pair(2,"y");
 p3 = make_pair(3,"t");
 p4 = make_pair(3,"z");
 m.insert(p1);
 m.insert(p2);
 m.insert(p3);
 cout<<m[3]<<endl;
 map<int,string>::iterator it;
 if( (it = m.find(3)) != m.end())
 {
     it->second = "z";
 }else
 {
     m.insert(p4);
 }
 cout<<m[3]<<endl;
}