How to retrieve value type from iterator in C++?

Question

My question is sure a simple one for anybody familiar with C++ syntax. I\'m just learning c++ and this is some sort of homework.

template

        

Answer 1

This will also work starting c++ 11:

typename Iter::value_type

So you do not have to type the whole std::iterator_traits thing.

Answer 2

The answer of Steve is right; in C++98, you have to use std::iterator_traits or you can use Iter::value_type if you know that the iterator has this typedef (e.g. is derived from std::iterator). However, there is another problem in your code: you normally can't simply divide iterators. This works with pointers, of course, but not in the more general case. A more general approach would be:

Iter itPivot = std::advance(begin, std::distance(begin, end)/2);

Answer 3

typename std::iterator_traits<Iter>::value_type

This will work if your template is instantiated with Iter as a pointer type.

By the way, typename isn't part of the type itself. It tells the compiler that value_type really is a type. If it was the name of a function or a static data member, then that affects the syntax. The compiler doesn't necessarily know what it is, since the specialization of iterator_traits for Iter might not be visible when the template is compiled.