CODEWITHSUNDEEP
c++overloadingoperator-keyword
jonjohnson
jonjohnson

Reputation: 423

Operator oveloading comparing two values from

I am learning the operator overloading functionality in C++ and I have come accross a problem. Here is my code: 

template <typename T>
class W
{
public:

    bool operator==(W&);
    T x;
};


template <typename T>
bool W<T>::operator==(W& w2)
{
    printf("\n%d, %d\n", x, w2.x);
    if(x == w2.x) return true;
    else return false;
}

int main()
{
    W<int>* w1 = new W<int>;
    W<int>* w2 = new W<int>;

    w1->x = 10;
    w2->x = 10;

    if(w1 == w2) printf("same");
    else printf("not");
}

The result is however 'not'. And the printf function is not called in the overloaded bool function. If I initialize the objects this way:

W<int> w1;
W<int> w2;

w1.x = 10;
w2.x = 10;

it works. But in my case I only use the first example objects (in my other project). So my question is how do I pass objects and it would work. Thanks.

Upvotes: 0

Views: 128

Answers (3)

Vlad from Moscow
Vlad from Moscow

Reputation: 311156

Your definition of the operator is not good. The better its declaration could look the following eay

bool operator==( const W &) const;

and corresponding realization

template <typename T>
bool W<T>::operator ==( const W &w2 ) const
{
    printf("\n%d, %d\n", x, w2.x);
    return ( x == w2.x );
}

In your code you compare pointers but must compare objects theirself. So the correct syntax will be

if ( *w1 == *w2 ) ...

Upvotes: 0

Zac Howland
Zac Howland

Reputation: 15870

You are not comparing objects in your code, but addresses to objects (pointers). There is no need for these objects to be dynamically allocated:

int main()
{
    W<int> w1;
    W<int> w2;

    w1.x = 10;
    w2.x = 10;

    if(w1 == w2)
        printf("same");
    else 
        printf("not");
}

Additionally, you can change your return value from your overloaded operator:

template <typename T>
bool W<T>::operator==(const W& w2) const // note:  it should be declared as const
{
    printf("\n%d, %d\n", x, w2.x);
    return x == w2.x;
}

Upvotes: 2

Luchian Grigore
Luchian Grigore

Reputation: 258678

You're comparing pointers, not objects, so your operator is never called.

Do

*w1 == *w2

or

w1->operator==(*w2);

Or no dynamic allocation at all

W<int> w1;
W<int> w2;

w1.x = 10;
w2.x = 10;

Also note that the signature for operator== should be

bool operator==(const W&) const

since it modifies neither of the operands.

Upvotes: 4

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