map的坑

#include<iostream>
#include<unordered_map>
using namespace std;
int main(){
std::unordered_map<int,int> mm;
mm[3];
mm.insert(pair<int,int>(1,2));
mm.insert(pair<int,int>(1,5));
mm.insert(pair<int,int>(2,3));
for(auto it = mm.begin(); it != mm.end();it ++ ){
cout << it->first << " : " << it->second << endl;
}
return 0;
}

1.[]操作符

2.map特性：Inserts element(s) into the container, if the container doesn't already contain an element with an equivalent key.