没想通的关于复制构造函数C++代码: A obj=func()

class A
{
public:
    A(int x=0):i(x)
    {
        cout << "Normal Contructor: " << i << endl;
    }
    
    ~A()
    {
        cout << "Destructor: " << i << endl;
    }
    
    A(const A & x)
    {
        cout << "Copy Constructor: " << i << endl;
    }
    
    A & operator=(const A & x)
    {
        cout << "Operator = " << endl;
        return *this;
    }


    int i;
    
};

A fun ()
{
    A t(2);
    return t;
}

int main()
{
    A a(1);
    
    A b = fun();
    //fun();
    
    cout << "end of program" << endl;
    
    return 0;
}

  上面main()函数执行后的输出为：

  Normal Contructor: 1
  Normal Contructor: 2
  end of program
  Destructor: 2
  Destructor: 1

int main()
{
    A a(1);
    
    //A b = fun();
    fun();
    
    cout << "end of program" << endl;
    
    return 0;
}

输出为：

Normal Contructor: 1
Normal Contructor: 2
Destructor: 2
end of program
Destructor: 1