Question

Consider the following :

class A
{
public:
    int xx;
    A(const A& other)
    {
        cout << "A cctor" << endl;
        /*  do some stuff */
    }

    A(int x) : xx(x) {}  /* conversion constructor */

    };


int main()
{    
    A a = 1;
    A other = a;
    return 0;
}

Is it right to say that CCtor converts from const to non-const in this case (and also in general) ?

Thanks ,Ron

Answer 1

No idea what you mean. A(const A&) is a typical copy-ctor, which has a “read-only” access to its only argument. If you pass anything const, everything is fine. If you pass anything non-const, for ctor it becomes const. A a = 1 is a conversion ctor, as you said. A other = a is a copy ctor. What’s the question?

Regarding your question’s title, in C++ there’s no fair way to convert const to non-const.

class A
{
public:
    int xx;
    A(const A& other)
    {
        cout << "A cctor" << endl;
        /*  do some stuff */
        // other is const here - you can only call its
        // const methods and read all its data members            
    }

    A(int x) : xx(x) {}  /* conversion constructor */
        // at this point, x is not const, but it's a copy
        // of an object you've passed here, not the object itself
        // you can change x, it just doesn't matter - you
        // change the copy
    };


int main()
{    
    A a = 1; // a is not const, 1 is passed "by value", since it's primitive type
    A other = a; // a is not const, other is not const, a is passed by const reference
    return 0;
}