Question

I compile the c++ code using the follow command to disable return value.
g++ -fno-elide-constructors rvoptimazation.cpp -o test
But the output of ./test is
10
10
10
13
0xbfdf0020
13
I am confused by the last call of the constructor. Can anyone explain which line of the code will call the constructor after return in operator*? Thanks in advance.

#include<iostream>    

using namespace std;  

class Rational{  
public:  
    Rational(int x ,int y){  
        _a = x;  
        _b = y;  
        cout << __LINE__ << endl;  
    }  
    Rational(Rational const &t){  
        cout << __LINE__ << endl;  
    }  
    Rational operator*(Rational const &t){  
        Rational re = Rational(_a * t._a ,_b * t._b);  
        cout << &re << endl;  
        return re;  
        //return *this;  
    }  
    Rational get()  
    {  
        return *this;  
    }  
public:  
    int _a ,_b;  
};  

int main()  
{  
    Rational r1(1 ,2);  
    Rational r2(2 ,3);  
    r1 * r2;  
 // cout << &r3 << endl;  
}  

Answer 1

operator* returns by value, so the returned object must be constructed. The statement return re calls the copy constructor to do that.

I think the explanation at Return value optimization is quite clear.