c++ 对象复制引用时何时调用构造函数、析构函数

class TEST{
    private :

    public :
        TEST() {std::cout << "constructor" << std::endl; }
        ~TEST() {std::cout << "destructor" << std::endl; }

};

class TEST fun(void)
{
    TEST t, tt;

    return t;
}

int main()
{

    class TEST t = fun();

    std::cout << "test...test" << std::endl;

}

$ ./pointer_reference
constructor
constructor
destructor
test...test
destructor //main函数中创建 t 实际上就是复制

class TEST{
    private :

    public :
        TEST() {std::cout << "constructor" << std::endl; }
        ~TEST() {std::cout << "destructor" << std::endl; }

};

class TEST fun(void)
{
    TEST t;

    TEST tt = t;

    return t;
}

int main()
{

    class TEST t = fun();

    std::cout << "test...test" << std::endl;

}

$ ./pointer_reference
constructor
destructor  //创建tt时候没有调用构造函数
test...test
destructor  //t 最后被释放

class TEST{
    private :

    public :
        TEST() {std::cout << "constructor" << std::endl; }
        ~TEST() {std::cout << "destructor" << std::endl; }

};

#if 0     //case 0
void fun(class TEST t)
#else    //case 1
void fun(class TEST& t)
#endif
{
    return;
}

int main()
{
    class TEST t;

    fun(t);

    std::cout << "test...test" << std::endl;

}

case 0:

$ ./pointer_reference
constructor
destructor
test...test
destructor

case 1:

$ ./pointer_reference
constructor
test...test
destructor