C++中map用Insert如果原来有值并不会覆盖

C++用Insert如果原来有值并不会覆盖，记得清空
或者直接用Map[key]=value来弄

#include<bits/stdc++.h>
using namespace std;
int main(){
    map<int,int>M;
    M[2]=3;
    M.insert({3,4});
    for(auto &x:M){
        cout<<x.first<<" "
        <<x.second<<endl;
    }
    M.insert({2,5});
    M.insert({3,4});
    M.insert({3,4});
    M.insert({3,6});
    for(auto &x:M){
        cout<<x.first<<" "
        <<x.second<<endl;
    }
    M[3]=8;
    for(auto &x:M){
        cout<<x.first<<" "
        <<x.second<<endl;
    }
}

输出