为什么我的对象看起来好像被销毁了两次？

Question

我阅读了一些关于 C++ 中指针的内容，并且不应该将所有内容都创建为指针。为了进一步了解这一点并了解它是如何工作的，我编写了一个小程序：

一个main.cpp

#include <iostream>

#include "Master.h"

using namespace std;

int main()
{
    Master master = Master("master");

    master.printSlaves();

    return 0;
}

一个Master.h

class Master
{
public:
    Master(std::string name);

    ~Master();

    void printSlaves()
    {
        _slave1.printName();
        _slave2->printName();
    }

private:
    Slave   _slave1;
    Slave   *_slave2;

    std::string _name;
};

还有一个Master.cpp

#include "Master.h"

Master::Master(std::string name)
{
    std::cout << "Master() entered." << std::endl;
    _name = name;

    _slave2 = new Slave("slave2");
    _slave1 = Slave("slave1");

    std::cout << "\t" << _name << " created." << std::endl;

    std::cout << "Master() exited." << std::endl;

}

Master::~Master()
{
    std::cout << "\t" << _name << " destroyed." << std::endl;
}

和Slave.h

class Slave
{
public:
    Slave()
    {

    }

    Slave(std::string name);

    void printName()
    {
        std::cout << "my name is " << _name << std::endl;
    }

    ~Slave();

private:
    std::string _name;
};

和Slave.cpp

#include "Slave.h"

Slave::Slave(std::string name)
{
    std::cout << "Slave() entered." << std::endl;

    _name = name;

    std::cout << "\t" << _name << " created." << std::endl;

    std::cout << "Slave() exited." << std::endl;


}

Slave::~Slave()
{
    std::cout << "\t" << _name << " destroyed." << std::endl;
}

我期望的输出：

Master() entered. Slave() entered. slave2 created. Slave() exited. Slave() entered. slave1 created. Slave() exited. master created. Master() exited. my name is slave1 my name is slave2 master destroyed. slave1 destroyed.

但我得到了

Master() entered. Slave() entered. slave2 created. Slave() exited. Slave() entered. slave1 created. Slave() exited. **slave1 destroyed.** master created. Master() exited. my name is slave1 my name is slave2 master destroyed. **slave1 destroyed.**

显然我的slave1 被销毁了两次。我不明白为什么会这样，为什么这甚至是可能的。

谁能给我解释一下？

Answer 1

问题出在一行

_slave1 = Slave("slave1");

为零件Slave("slave1");创建一个临时从站，然后分配给_slave1。赋值后，临时的Slave对象被销毁。

如果你写你的代码像

Master::Master(std::string name):_slave1("slave1")
{
 //other code
}

那么它只会被创建和销毁一次。