Linked list const iterator

Question

I have implemented a doubly-linked list, and created an iterator which extends std::iterator. I'm now trying to create a const version.

I tried:

typename typedef list_iterator<T_>        iterator;
typename typedef list_iterator<T_> const  const_iterator;

If I do this though, I get this error:

error C2678: binary '--' : no operator found which takes a left-hand operand of type 'const    list_iterator<T_>' (or there is no acceptable conversion)

Here is my operator--:

list_iterator& operator -- ()
{
    _current = _current->_previous;
    return *this;
}

list_iterator operator--(int) // postfix
{
    list_iterator hold = *this;
    --*this;
    return list_iterator( hold );
}

If I put

list_iterator operator--() const

... I'm not able to modify the value of _current

How do I make my iterator now work like a const_iterator so that from my linked list I can call get the const version of begin() and end(), as well as cbegin() and cend()?

a const_iterator and a const iterator are VERY different things. They actually need to be two different types, sorry. It's the difference between "a constant pointer to data", and "a pointer to constant data" — Mooing Duck
– Mooing Duck, Commented Feb 19, 2014 at 19:59

Community · Accepted Answer · 2017-05-23 10:31:56Z

2

Right. The problem is your declaration of your const_iterator typedef. (See How to correctly implement custom iterators and const_iterators? )

Instead of

typename typedef list_iterator<T_> const  const_iterator;

you want

typename typedef list_iterator<const  T_> const_iterator;

edited May 23, 2017 at 10:31

CommunityBot

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answered Feb 19, 2014 at 19:59

m24p

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