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 learning C++ and this is some sort of homework.

template<typename Iter> void quickSort(Iter begin, Iter end) {             //..     auto pivot = * ( begin + (end - begin)/2 );     //.. } 

pivot is supposed to contain the value from the center of the interval [begin, end].

The code I wrote there works, but auto is a keyword from the new C++11 language standard. How to do it the old-way? What do I write instead of auto?

Answer 1

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.

Answer 2

This will also work starting c++ 11:

typename Iter::value_type 

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