Extending iterators in C++

Question

I'm trying to implement an iterator which encapsulates another iterator and performs range checking. Therefore I'm extending from that Iterator like so:

 template<typename ITERATOR_T>
 class r_iterator : public ITERATOR_T {

     //...

     r_iterator (ITERATOR_T begin, ITERATOR_T end) {
         this->begin = begin;
         this->end = end;
    }
 };

I want to use the iterators that are passed in the constructor to perform the range checking. My idea is to set the thing to which the "this"-iterator (i.e. r_iterator) points to to the element which is pointed to by the "begin" iterator from the constructor. This I would like to do so I can override certain methods like operator++ for example, perform range checking and then call the super method of the class I'm extending.

I would thus like to know whether it is possible to somehow set the element the "this"-iterator (r_iterator) points to assuming that I'm extending some STL Iterator class.

I could unfortunately not find any information about that in the c++ reference.

Regards and Thank you

@user2820379: You can still use the concept if not the code. — MSalters, Dec 21 '13 at 15:37

score 1 · Accepted Answer · answered Dec 20 '13 at 23:15

There's no need to inherit, you can write a simple wrapper class like this:

#include <iostream>
#include <vector>
#include <stdexcept>

template <typename Iterator>
class MyIterator
{
    Iterator _begin;
    Iterator _end;
    Iterator _cur;
public:
    explicit MyIterator(Iterator begin, Iterator end)
        : _begin(begin), _end(end)
    {
        _cur = _begin;
    }

    bool has_next() const 
    {
        return (_cur != _end);
    }

    void operator++(int dummy) 
    { 
        if (!has_next())
            throw std::out_of_range("Out of range.");
        _cur++;
    }
};

int main(int argc, char* argv[]) 
{
    std::vector<int> v = {1, 2, 3};
    MyIterator<std::vector<int>::iterator> my_it(v.begin(), v.end());
    my_it++;
    my_it++;
    my_it++;
    my_it++;
    return 0;
}

You don't need `begin` if you're only implementing a forward iterator. A heavy-duty wrapper would inherit from `MyIteratorImpl::iterator_category>` which is specialized for all the categories. — MSalters, Dec 21 '13 at 15:35

Extending iterators in C++

1 Answers1