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

Do this:

// defined in boost/utility.hpp, by the way
template 
Iter next(Iter iter)
{
    return ++iter;
}

// first check we aren't going to kill ourselves
// then check if the iterator after itr is the end
if ((itr != Mine.end()) && (next(itr) == Mine.end()))
{
    // points at the last element
}

That is all. Never gives you undefined behavior, works on all iterators, good day.

Wrap it up for fun:

template 
bool is_last(Iter iter, const Cont& cont)
{
    return (iter != cont.end()) && (next(iter) == cont.end())
}

Giving:

if (is_last(itr, Mine))

---

If you're allergic to utility functions/nice looking code, do:

if ((itr != Mine.end()) && (itr + 1 == Mine.end()))

But you can't do it on non-random-access iterators. This one works with bidirectional iterators:

if ((itr != Mine.end()) && (itr == --Mine.end()))

And is safe since end() > itr by the first check.