现代c++vector的emplace_back成员函数

现代c++标准库中vector容器的emplace_back方法

一言以蔽之，emplace_back是c++11引入的vector成员函数，用于在vector末尾直接构造元素，而不是先构造再拷贝或移动

基本用法

std::vector<MyClass>vec;
vec.emplace_back(args...);

与push_back的区别

1. 构造方式
   • push_back：先构造临时对象，然后拷贝或移动到容器中
   • emplace_back：直接在容器内存中构造对象
2. emplace_back更高效

示例

#include <vector>
#include <string>
#include <iostream>

class Person {
public:
    Person(std::string name, int age) : name_(name), age_(age) {
        std::cout << "Constructing " << name_ << "\n";
    }
    
    Person(const Person& other) : name_(other.name_), age_(other.age_) {
        std::cout << "Copying " << name_ << "\n";
    }
    
    Person(Person&& other) noexcept : name_(std::move(other.name_)), age_(other.age_) {
        std::cout << "Moving " << name_ << "\n";
    }

private:
    std::string name_;
    int age_;
};

int main() {
    std::vector<Person> people;
    
    // 使用push_back
    std::cout << "Using push_back:\n";
    people.push_back(Person("Alice", 30));
    // 输出:
    // Constructing Alice (临时对象)
    // Moving Alice (移动到vector中)
    
    // 使用emplace_back
    std::cout << "\nUsing emplace_back:\n";
    people.emplace_back("Bob", 25);
    // 输出:
    // Constructing Bob (直接在vector中构造)
    
    return 0;
}