526互联

vector的push_back与emplace_back

发布时间 2023-07-17 13:01:30作者: devin1024

为什么需要将移动构造函数和移动赋值运算符标记为noexcept

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

class A1 {
public:
    A1() { cout << "ctor" << endl; }
    A1(const A1 &other) { cout << "cp-ctor" << endl; }
    A1& operator=(const A1 &other) { cout << "cp-eqop" << endl; return *this; }
    A1(A1 &&other) noexcept { cout << "mv-ctor" << endl; } // noexcept is necessary!
    A1& operator=(A1 &&other) noexcept { cout << "mv-eqop" << endl; return *this; }

    int num = 100;
};

int main() {
    vector<A1> arr;
    A1 a1;

    cout << "---- test push_back ----" << endl;
    arr.push_back(a1);

    cout << "---- test emplace_back ----" << endl;
    arr.emplace_back(a1);
}

// output:

// ctor
// ---- test push_back ----
// cp-ctor
// ---- test emplace_back ----
// cp-ctor
// mv-ctor