C++: overloading "pointer to object" * operator

Question

I was some misunderstanding about default operator definition(by compiler).

I have small class:

class Q
{
public:
    Q() {};
    Q(int i) { x = i; };
    ~Q() {};
    void print() { cout << x << endl; };
    Q& operator * ()
    {
        cout << "operator *\n";
        return *this;
    };
    const Q& operator * () const
    {
        cout << "operator *\n";
        return *this;
    };
private:
    int x;
};

And i'm doing this whit it:

int main()
{
    Q* obj_p = new Q(1);
    Q obj = *obj_p;
    obj.print();
    return 0;
}

I expected to see operator *, before 1. But I saw only print() method result.

What does it mean? That I don't need to overload operator * - it's compiler work or that I do overloading somehow wrong?

Thanks.

juanchopanza · Accepted Answer · 2014-08-04 09:08:15Z

4

obj_p is a pointer. You have not overloaded (and cannot do it anyway) the de-reference operator for a pointer. To invoke your overload, you need to act on an instance:

Q obj;
*obj;

answered Aug 4, 2014 at 9:08

juanchopanza

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2 Comments

Kirill Timofeev Over a year ago

And can you tell me, please: what about 'new' operator.<br> Should I overload it(in simple cases, not so simple like that, but still)? Or compiler will allocate exactly as much memory for my class as I need?

James Kanze Over a year ago

@KirillTimofeev You need to overload the operator new function if, and only if, your class needs some special allocation (typically, a pool allocator, or some such). Such cases are rare.

Luchian Grigore · Accepted Answer · 2014-08-04 09:08:23Z

1

There's no user-defined operator called - obj_p is a pointer, not an object, so the built-in dereference operator is called.

To complete juanchopanza's answer, you can call your operator on a pointer like so:

Q* obj_p = new Q(1);
Q obj = obj_p->operator*();

answered Aug 4, 2014 at 9:08

Luchian Grigore

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Comments

oknsnl · Accepted Answer · 2014-08-04 09:31:00Z

0

You use your '*' operator on Q pointer but you should use on Q objects. if you try *(*obj_p) you will see.

answered Aug 4, 2014 at 9:31

oknsnl

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