为什么此函子会两次调用析构函数? [英] Why the destructors are called twice for this functor?

问题描述

当我运行以下程序时，析构函数被调用两次，而我试图理解为什么?

When I run the following program, the destructor is called twice and I'm trying to understand why?

#include <iostream>
#include <vector>
#include <algorithm>

class sample
{
    public:
        sample() { std::cout << "Constructor " << std::endl; }

        ~sample() { std::cout << "Destructor" << std::endl; }

        void operator()(int i)
        {
            std::cout << i << " , "  << std::endl;
        }
};

int main()
{

    std::vector<int> iNumbers;

    for ( int i = 0 ; i < 5 ; ++i)
        iNumbers.push_back(i);

    std::for_each(iNumbers.begin() , iNumbers.end() , sample() );
}

输出如下所示

Constructor
0 ,
1 ,
2 ,
3 ,
4 ,
Destructor
Destructor

推荐答案

三个违反的经典规则.试试这个:

Classic rule of three violation. Try this:

#include <iostream>
#include <vector>
#include <algorithm>

class sample
{
    public:
        sample() { std::cout << "Constructor " << std::endl; }

        sample(const sample&) { std::cout << "Constructor (copy)" << std::endl; }

        ~sample() { std::cout << "Destructor" << std::endl; }

        sample& operator=(const sample&) { return *this; }

        void operator()(int i)
        {
                std::cout << i << " , "  << std::endl;
        }
};

int main()
{
    std::vector<int> iNumbers;

    for ( int i = 0 ; i < 5 ; ++i)
            iNumbers.push_back(i);

    std::for_each(iNumbers.begin() , iNumbers.end() , sample() );
}

输出为:

构造函数
0，
1，
2，
3，
4，
构造函数(副本)
析构函数
析构函数

Constructor
0 ,
1 ,
2 ,
3 ,
4 ,
Constructor (copy)
Destructor
Destructor

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