Thread: Simple code: Can 2 references refer to the same object?

I was told that C++ does not allow 2 references refer to the same object. So I wrote a snippet to verify it:

Code:

class Base{                                                                                                                                                                  
    string& s;                                                                                                                                                               
public:                                                                                                                                                                      
    Base(string a):s(a){}                                                                                                                                                    
    ~Base(){cout<<"Base"<<endl;}                                                                                                                                             
};                                                                                                                                                                           
                                                                                                                                                                             
                                                                                                                                                                             
int main(int argc, char* argv[]){  
    string b = "asdfa";  
    string a="abc";
    Base x(a);
    Base y(b);
    y = x;
}

Complier reports error:

main.cc: In member function `Base& Base:perator=(const Base&)':
main.cc:30: error: non-static reference member `std::string&Base::s', can't use
default assignment operator

This is what I expected: 2 references CAN NOT refer to the same object.

But then I wrote another snippet:

Code:

    string a = "abc";                                                                                                                                                        
    string b = "asdfa";                                                                                                                                                      
    string& x = a;                                                                                                                                                           
    string& y = x;                                                                                                                                                           
    y=x;                                                                                                                                                                     
    cout<<y<<endl;                                                                                                                                                           
    x[0]='X';                                                                                                                                                                
    cout<<y<<endl;

It seems that this code DOES work. and both x and y refer to the same string. As you modified x to "Xbc", y's value is also changed. How come?!

Who says you can't have 2 references pointing to the same object?

Two references can point to the same object.

A reference cannot point to two different objects, that might be what you were told.

That is why the first example fails. When you assign the Base object called x to the base object called y, the compiler generated copy assignment operator is used. That does a member-wise copy. But for a reference, you cannot re-assign it to another object, so the reference member of y cannot have another object assigned to it. That's why you get an error about the default assignment operator.