Creating custom random access iterator in C++ 2011

Question

I would like an opinion on my code. I need a random access iterator for my custom container. If I read the C++ 2011 standard, specially chapter 24, I understood that an implementation could be the following:

class my_iterator : public std::iterator<std::random_access_iterator_tag, my_element>
{
    private:
       my_container *_ref;
       my_iterator_state state; // some useful state
    public:
       my_iterator ();
       my_iterator (const my_iterator &);
       my_iterator (my_iterator &&);
       ~my_iterator ();
       my_iterator &operator = (const my_iterator &);
       my_iterator &operator = (my_iterator &&);
       reference operator * ();
       my_iterator &operator ++ ();
       bool operator != (my_iterator);
       value_type operator * ();
       pointer operator -> ();
       my_iterator &operator * ();
       void operator ++ (int);
       value_type operator ++ (int);
       const my_iterator &operator ++ (int);
       reference operator ++ (int);
       my_iterator &operator -- ();
       const my_iterator operator -- (int);
       reference operator -- (int);
       my_iterator &operator += (difference_type);
       my_iterator operator + (difference_type);
       my_iterator operator - (difference_type);
       reference operator [] (difference_type);
       bool operator < (my_iterator);
       bool operator > (my_iterator);
       bool operator <= (my_iterator);
       bool operator >= (my_iterator);
       friend difference_type (my_iterator, my_iterator);
       friend my_iterator operator + (difference_type, my_iterator);
       friend void swap (iterator &, iterator &);
};

void swap (iterator &, iterator &);
difference_type (my_iterator, my_iterator);
my_iterator operator + (difference_type, my_iterator);

The above implementation is correct and full-featured? There are too members?

Oh gawd, yeah. Please do yourself a service and use `boost::iterator_facade`. — R. Martinho Fernandes, May 10 '13 at 14:31
Welcome to Stack Overflow. Please take the time to read the [faq]. You'll get a [badge](http://stackoverflow.com/badges) (c: — Peter Wood, May 10 '13 at 14:32
@Alessio Well, do you want me to give you the bad news first or... wait, there are no good news. — R. Martinho Fernandes, May 10 '13 at 14:44
Well, the above doesn't even compile, which makes it difficult to be a valid random access iterator. http://ideone.com/FBPu0f (and it isn't just `my_element`) Do you want us to fix your typos as well as audit your random access ness? — Yakk - Adam Nevraumont, May 10 '13 at 15:08
http://stackoverflow.com/questions/8054273/how-to-implement-an-stl-style-iterator-and-avoid-common-pitfalls/8054856#8054856 — Mooing Duck, May 10 '13 at 18:07
@Yakk No, no, I don't need any help to correct my typos; I was reading the standard to analyze the iterator concept. — Alessio G. B., May 10 '13 at 18:12

score 3 · Accepted Answer · answered May 10 '13 at 15:29

In general, you can't have overloads with the same arguments but different return types, so several of your members can't exist. You should keep the following:

reference operator * ();
my_iterator operator ++ (int);
my_iterator operator -- (int);

and remove the bogus overloads:

value_type operator * ();
void operator ++ (int);
value_type operator ++ (int);
const my_iterator &operator ++ (int);
reference operator ++ (int);
const my_iterator operator -- (int);
reference operator -- (int);

This makes no sense:

friend difference_type (my_iterator, my_iterator);

which I assume should be:

friend difference_type operator-(my_iterator, my_iterator);

and you seem to be missing operator-=

indeed `friend difference_type (my_iterator, my_iterator);` is a typing error :) — Alessio G. B., May 10 '13 at 18:02

Creating custom random access iterator in C++ 2011

1 Answers1