CODEWITHSUNDEEP
c++linked-listiterator
ANBHOO
ANBHOO

Reputation: 135

Understanding iterator class in c++

Recently in class we were taught about the STL iterator to traverse through lists. In the example code given for a basic Iterator for a linked list I came across something that I couldn't make sense of.

We were given 2 Iterator classes, const_iterator and iterator. They were both sub-classes of the List class. iterator inherited from const_iterator. In the constructor of iterator I'm not sure why it was written like this;

iterator class:

class iterator:public const_iterator{ 
    friend sortedList
protected:
    iterator(Node* n):const_iterator(n){}
public:
    iterator(){ 
        n = nullptr;
    }

The const_iterator class: 

    class const_iterator { 
    friend SortedList 
protected:
    Node* curr_;
    const_iterator(Node* n){ 
        curr_ = n; 
    }
public:
    const_iterator(){
        curr_ = nullptr;
    }

My question is why does iterator inherit from const_iterator and why is iterator's constructor initializing the const_iterator ctor and doing nothing to itself.

Side question; when accessing curr_ from iterator how would I refer to it? Would I just call curr_ or would I use this->curr_?

Upvotes: 0

Views: 108

Answers (1)

Bo Persson
Bo Persson

Reputation: 92261

My question is why does iterator inherit from const_iterator and why is iterator's constructor initializing the const_iterator ctor and doing nothing to itself.

There is a requirement for the standard containers that iteratoris convertible to const_iterator. Deriving one from the other is one way of achieving this.

The const_iterator base class stores a pointer to a Node but the iterator does not, so passing the parameter on to the base class will initialize the curr_ member that both base and derived can use.

when accessing curr_ from iterator how would I refer to it? Would I just call curr_ or would I use this->curr_?

You can use curr_ both in the base class and the derived as long as there is no question about whether it is a member variable or not. The fact that the name ends in an underscore is a common convention for member variable names.

If there is any doubt about he scope, you can use this->member to make it obvious that you refer to a member of the class.

Using this-> when it really isn't needed is deemed extra confusing by some people (like me) so should probably be saved for cases where there is a real need to disambiguate a name.

Upvotes: 2

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