Why doesn't my custom iterator work with the STL copy?

Question

I wrote an OutputIterator for an answer to another question. Here it is:

#include 

using namespace std;

template< typename T, typename U &g         


        

Answer 1

#include 
#include 
#include 
#include 

using namespace std;

template< typename T, typename U >
class queue_inserter
{
    queue &qu;

public:
    // for iterator_traits to refer
    typedef output_iterator_tag iterator_category;
    typedef T value_type;
    typedef ptrdiff_t difference_type;
    typedef T* pointer;
    typedef T& reference;

    queue_inserter(queue &q) : qu(q) { }
    queue_inserter& operator ++ () { return *this; }
    queue_inserter operator * () { return *this; }
    void operator = (const T &val) { qu.push(val); }
};

template< typename T, typename U >
queue_inserter make_queue_inserter(queue &q)
{
    return queue_inserter(q);
}

int main()
{
    // uses initalizer list (C++0x), pass -std=c++0x to g++
    vector v({1, 2, 3});
    queue> q;
    copy(v.cbegin(), v.cend(), make_queue_inserter(q));
    while (!q.empty())
    {
        cout << q.front() << endl;
        q.pop();
    }
}

This should do it with iterator_traits; a helper struct in which defines all types an iterator should typically define. Functions in , refer to these types when required like iterator_traits::iterator_category or say iterator_traits::value_type, etc. Just defining them inside one's custom iterator would do the trick. This is the modern way of writing iterators, as opposed to the classical way of inheriting from std::iterator. Having a look at reveals that even std::iterator defines these types i.e. iterator_category, difference_type, etc. This is the reason, when inherited from std::iterator, the derived iterator class gets these due to heredity.