Mayank Jain - 1 year ago 65

C++ Question

I am trying to implement

`->`

My Iterator class and MapNode are defined like:

`template <typename Key_T,typename Mapped_T>`

class Map<Key_T,Mapped_T>::Iterator

{

MapNode<Key_T,Mapped_T>* curr;

}

template <typename Key_T,typename Mapped_T>

class MapNode

{

Key_T key;

Mapped_T value;

MapNode *up,*down,*prev,*next;

friend class Map<Key_T,Mapped_T>;

};

Now I want to overload operator->, but the problem is I am not exactly getting how to return pointer of pair of key and value where iterator is currently pointing:

My current implementation is :

`template <typename Key_T,typename Mapped_T>`

std::pair<const Key_T, Mapped_T>*

Map<Key_T,Mapped_T>::Iterator::operator->() const

{

const Key_T currKey = (this->curr)->key;

const Mapped_T currVal = (this->curr)->value;

ValueType* vt = new ValueType(std::make_pair(currKey,currVal));

return vt;

}

But I am afraid that this will cause memory leaks as the ValueType pointer memory won't be deallocated ever.

Can someone guide me on how can this be done correctly?

Please help.

`[ValueType is defined as std::pair<const Key_T, Mapped_T>]`

Answer Source

I would start by storing the values in the MapNode in an `std::pair`

:

```
template <typename Key_T,typename Mapped_T>
class MapNode
{
std::pair<Key_T, Mapped_T> value;
MapNode *up,*down,*prev,*next;
friend class Map<Key_T,Mapped_T>;
};
```

Then the iterator can just return the address of that pair.

```
template <typename Key_T,typename Mapped_T>
std::pair<const Key_T, Mapped_T> *
Map<Key_T,Mapped_T>::Iterator::operator->() const
{
using ptr = std::pair<const Key_T, Mapped_T> *;
return (ptr)(&(curr->value));
}
```

The cast is a little ugly, but that's why you encapsulate it inside a piece of code you rarely have to look at.