std::vector::push_back()

定义:

void push_back (const value_type& val);

作用:

Add element at the end
Adds a new element at the end of the vector, after its current last element. The content of val is copied (or moved) to the new element.

注意:

This effectively increases the container size by one, which causes an automatic reallocation of the allocated storage space if -and only if- the new vector size surpasses the current vector capacity.

说明:

如果是push_back(container),会发生容器元素的复制 (这里的container指的是vector、map...)

参考---cplusplus.com

实验1:

源码:

#include<iostream>
#include<vector>
using namespace std;

int main() {
    vector<vector<int>> res;
    vector<int> v1;
    v1.push_back(1);
    v1.push_back(2);
    vector<int>& v=v1;
    v.push_back(5);
    cout<<"v1:"<<endl;
    for(int i:v1) {
        cout<<i<<endl;
    }
    res.push_back(v1);
    cout<<"after push 7:"<<endl;
    v.push_back(7);
    cout<<"res[0:]"<<endl;
    for(int i:res[0]) {
        cout<<i<<endl;
    }
    cout<<"v1:"<<endl;
    for(int i:v1) {
        cout<<i<<endl;
    }
    return 0;
}

结果:

实验二:

源码:

#include<iostream>
#include<map>
#include<vector>
using namespace std;
int main() {
    vector<map<int,int>> v;
    map<int,int> mp1;
    mp1.insert(std::pair<int,int>(1,1));
    mp1.insert(std::pair<int,int>(2,2));
    cout<<"mp1:"<<endl;
    for(std::pair<int,int> e:mp1) {
        cout<<e.first<<" "<<e.second<<endl;
    }
    v.push_back(mp1);
    mp1.insert(std::pair<int,int>(3,3));
    cout<<"after push_back:"<<endl;
    cout<<"mp1:"<<endl;
    for(std::pair<int,int> e:mp1) {
        cout<<e.first<<" "<<e.second<<endl;
    }
    cout<<"v[0]:"<<endl;
    for(std::pair<int,int> e:v[0]) {
        cout<<e.first<<" "<<e.second<<endl;
    }

    return 0;
}

结果: