Life is short, use emplace_back()。探究一下C++11的push_back, move, rvalue, emplace_back

前言

一直以来写代码，vector想都没想就是push_back，今天发现的C++11的emplace_back碾压了传统的push_back

总结一句话：Life is short, use emplace_back()。

简单叙述原因：emplace_back可以“同时构造和插入，一次搞定”，push_back需要“先构造，后插入，而且插入的时候还伴随着拷贝或者移动”。

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Talk is cheap, show me the code

#include <iostream>
#include <utility>
#include <chrono>
#include <vector>
#include <string>
using namespace std;
using namespace chrono;


int main()
{
    vector<string> v;
    int num = 100000;
    v.reserve(num);                    // capacity 一次性增大到十万，减少vector多次增大时候的拷贝次数

    cout << "push_back way one:     ";
    auto start = system_clock::now();
    for (int i = 0; i < num; ++i)
    {
        string temp("caitao");
        v.push_back(temp);             // push_back(const string&)，参数是左值引用
    }
    auto end = system_clock::now();
    auto duration = duration_cast<microseconds>(end - start);
    cout << duration.count() << " microseconds." << endl << endl;

    cout << "push_back way two:     ";
    v.clear();
    start = system_clock::now();
    for (int i = 0; i < num; ++i)
    {
        string temp("caitao");
        v.push_back(move(temp));       // push_ba