Overloading operator to use with another class in C++

Question

Is there any way to overload the > (greater than) operator, to be able to do something like:

myClass *a = new myClass(1);
myClass *b = new myClass(3);

if(a > b) //it should compare the int values from the constructors
  //do something

I've tried overloading the operator, but got various errors. I am using VC++.

It is not possible to overload operators where both of the arguments are primitive types. Pointers are primitive types. — Oliver Charlesworth
– Oliver Charlesworth, Commented Jul 2, 2012 at 23:00
If you use objects and not pointers. PS there is no need to use pointers in this example. — Loki Astari
– Loki Astari, Commented Jul 2, 2012 at 23:02
OK, then, no pointers, but still errors. It would be too much to paste the whole code in here... I can paste the error though. — Eduard Luca
– Eduard Luca, Commented Jul 2, 2012 at 23:04
I find this book good for how to do operator overloading, it covers each operator in turn and shows prescriptively how to do it. mindview.net/Books/TICPP/ThinkingInCPP2e.html Get the free e-book. — ctrl-alt-delor
– ctrl-alt-delor, Commented Jul 2, 2012 at 23:12

Matteo Italia · Accepted Answer · 2012-07-02 23:03:46Z

2

You cannot overload operators for pointers, because they are primitive types (and you cannot create an overload where both arguments are primitive types); instead, you can overload the operators for your objects of user-defined types (not pointer to them):

class myClass
{
    // ...
public:
    bool operator>(const myClass & right) const
    {
        return this->whatever()>right.whatever();
    }
};

myClass *a = new myClass(1);
myClass *b = new myClass(3);

if(*a > *b) //it should compare the int values from the constructors
  //do something

notice that, if you don't have a particular reason to allocate stuff on the heap, it's much better to just allocate it on the stack:

myClass a(1);
myClass b(3);
if(a > b)
    // do something

answered Jul 2, 2012 at 23:03

Matteo Italia

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3 Comments

Eduard Luca Over a year ago

OK, but I still get this error (Persoana is MyClass):

error C2679: binary '>' : no operator found which takes a right-hand operand of type 'const Persoana' (or there is no acceptable conversion) 1>          could be 'built-in C++ operator>(Persoana *, Persoana *)' 1>          while trying to match the argument list '(Persoana *, const Persoana)'

ildjarn Over a year ago

@Eduard : That indicates you're comparing a Persoana to a Persoana* -- neither should be a pointer.

Eduard Luca Over a year ago

Got it to work. It was from a header file that I didn't write, it was using my class as a template, and had a pointer to it. Thanks a million!

Loki Astari · Accepted Answer · 2012-07-02 23:04:18Z

2

Try

class MyClass
{
    int value;
    public:
        bool operator>(MyClass const& rhs) const
        {
             return value > rhs.value;
        }

        MyClass(int v):value(v){}

};

int main()
{
     MyClass a(1);
     MyClass b(3);

     if (a > b) { PLOP } else { POOP }
}

answered Jul 2, 2012 at 23:04

Loki Astari

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