iterator-traits

I am new to C++ so please bear with me. I am trying to understand STL iterator_traits. In the book "The C++ Standard Library" the structure iterator_traits is defined as follows: template <class T> struct iterator_traits{ typedef typename T::value_type value_type typedef typename T::difference_type difference_type typedef typename T::iterator_category iterator_category typedef typename T::pointer pointer typedef typename T::reference reference } So it seems to me that it is re-exposing the subtypes that T already exposes. Moving ahead further, the book gives an example of how to use it, which

I have the following code: template<typename T, typename Allocator = std::allocator<T> > class Carray { // ... typedef T* pointer; typedef pointer iterator; // ... }; Now I'm trying to do partial specialization for iterator_traits . It seems OK to me, but g++ 4.4.5 complains: #include <iterator> namespace std { template<typename T, typename Allocator> struct iterator_traits<typename Carray<T, Allocator>::iterator> { // line 128 typedef T value_type; typedef typename Allocator::difference_type difference_type; typedef typename Allocator::reference reference; typedef typename Allocator::pointer

I'd like to specialize std::iterator_traits<> for iterators of a container class template that does not have the usual nested typedefs (like value_type , difference_type , etc.) and whose source I shouldn't modify. Basically I'd like to do something like this: template <typename T> struct iterator_traits<typename Container<T>::iterator> { typedef T value_type; // etc. }; except that this doesn't work, as the compiler is unable to deduce T from Container<T>::iterator . Is there any working way to achieve the same? For example: template <typename T> class SomeContainerFromAThirdPartyLib {

C++17 introduced the concept of ContiguousIterator http://en.cppreference.com/w/cpp/iterator . However it doesn't seem that there are plans to have a contiguous_iterator_tag (in the same way we now have random_access_iterator_tag ) reported by std::iterator_traits<It>::iterator_category . Why is contiguous_iterator_tag missing? Is there a conventional protocol to determine if an iterator is Contiguous? Or a compile time test? In the past I mentioned that for containers if there is a .data() member that converts to a pointer to ::value type and there is .size() member convertible to pointer