handling reference member variable in assignmnet operator

[msgurikar]

Hi,
How do i handle reference member variable in assignment operator and copy constructor.

class A{
private:
int& a;
public:
A();
~A();
A(const A& a1);
A& operator=(const A& a1);
};

A::A():a(0){}
A::A(int& i): a(i)  //yes,, we have to do this
{
}

same way, how do i handle reference member variable in copy constructor and assignment operator implementation,

Regards

[Banfa]

The in copy constructor you just initialise the reference of the new object from the reference of the old object.

You treat it as an other member, you assign to it if you want to being aware that you will change the object being referenced not the reference itself.

[Banfa]

A::A(const A& a1) : a(a1.a)
{
}

A::A& operator=(const A& a1)
{
    a = a1.a; // If desired

    // ... rest of operator= code
}

[newb16]

A::A():a(0){}

this gives an error on gcc - it can't initialize the reference pointing to non-variable. And you also can't re-initialize the reference once it's initialized in constructor - so the assignment can't change it, only the variable it points to.

[msgurikar]

A& A::operator=(co nst A& a1)
{

a = a1.a // Is it a initialization or assigning
}


Is the above statmeent in assignment operator is initialization or assignmnet,
according to me its assignment, not initialization. I dont think reference can be assigned, hope the above will give comiler error.

Regards

[Banfa]

operator= is an operator and works on an object. Therefore the object already exists and since initialisation happens when the object is create and this object already exists this must be assignment.

a = a1.a;

Will not give a compiler error as since a and a1.a have the same type, int.

But like I (and you) said you can assign references so it will copy the object referenced by a1.a to the object referenced a rather than copy a1.a to a.

Also like I said you will have to decide if this is desirable behaviour but it is certainly valid code and it may be desirable behaviour.

If you need a reference that you can change in operator= then use a pointer rather than a reference or better yet a handle class.

[weaknessforcats]

And don't forget that in your copy constructors and assignment operators you cannot copy or assgn the object to itself. However, your user can code it that way. Be sure you test that this!= &of the other object. If it is, just return. Otherwise, go ahead and make the copy.