Testing whether an iterator points to the last item?

Question

I have an stl iterator resulting from a std::find() and wish to test whether it is the last element. One way to write this is as follows:

mine *match = some         


        

Answer 1

You would first need a way to determine if an iterator is a reverse one, which was ingeniously shown here :

#include 
#include 

template
struct is_reverse_iterator : std::false_type { };

template
struct is_reverse_iterator>
: std::integral_constant::value>
{ };

Then you could have two flavors for performing the test

template // for normal iterators
struct is_last_it
{
    template
    static bool apply(It it, Cont const &cont)
    { // you need to test with .end()
        return it != cont.end() && ++it == cont.end();
    }
};

template<> // for reverse iterators
struct is_last_it
{
    template
    static bool apply(It it, Cont const &cont)
    { // you need to test with .rend()
        return it != cont.rend() && ++it == cont.rend();
    }
};

And a single interface function

template
bool is_last_iterator(It it, Cont const &cont)
{
    return is_last_it::value>::apply(it, cont);
};

Then for every type of iterator (reverse / straight) you can use the interface function

int main()
{
    std::vector v;
    v.push_back(1);

    auto it (v.begin()),  ite(v.end());   // normal iterators
    auto rit(v.rbegin()), rite(v.rend()); // reverse iterators

    std::cout << is_last_iterator(it, v) << std::endl;
    std::cout << is_last_iterator(ite, v) << std::endl;
    std::cout << is_last_iterator(rit, v) << std::endl;
    std::cout << is_last_iterator(rite, v) << std::endl;

    return 0;
}

Note that some implementation (apart from std::begin() and std::end() which are common enough, also include std::rbegin() and std::rend(). When possible use this set of functions instead of member .begin() etc.