Non-member begin() and end()or C++11 iterator range accrss

Sven Johannsen14.08.2014

C++ User Group Aachen

Always use nonmember begin(x) and end(x)

“Always use nonmember begin(x) and end(x) (not x.begin() and x.end()), because begin(x) and end(x) are extensible and can be adapted to work with all container types – even arrays – not just containers that follow the STL style of providing x.begin() and x.end() member functions.”

Herb SutterElements of Modern C++ Style

From ISO 14882 - 2011

24.6.5 range access [iterator.range]…template <class C> auto begin(C& c) -> decltype(c.begin());template <class C> auto begin(const C& c) -> decltype(c.begin());

template <class C> auto end(C& c) -> decltype(c.end());template <class C> auto end(const C& c) -> decltype(c.end());…

From Boost

“A Range is a concept similar to the STL Container concept. A Range provides iterators for accessing a half-open range [first,one_past_last) of elements and provides information about the number of elements in the Range. However, a Range has fewer requirements than a Container.”

BoostRange / Overview

Differences between Container and Range

• (STL-) Container• begin() and end() member

functions

• auto it1 = cont.begin();

• auto it2 = cont.end();

• e.g. std::vector, std::list, std::map

Rangenon member begin() and end() functions

auto it1 = begin(cont);

auto it2 = end(cont);

e.g. std::vector, std::list, std::map and double[10], std::valarray

Non Member begin() and end()

Unified iterator access for any containerAddition level of abstraction for an iterator access.

template<class CONT> void foo(const CONT& cont) {for(auto it = begin(cont); it != end(cont); ++it) { cout << *it << " ";}

}

This code runs with any container (if non-member begin() and end() are overloaded).

Non-Member for Non-STL Container

E.g.: Range based for loop for non STL containers

template<class T> CArrayIterator<T> begin(const CArray<T>& arr);template<class T> CArrayIterator<T> end(const CArray<T>& arr); ...CArray<int> arr;...for(int i : arr) { cout << i << " " << endl;}bool sorted = std::is_sorted(begin(arr), end(arr));

C++14

C++14 will also introduce non-member • cbegin(), • cend(), • rbegin(), • rend(), • crbegin() and • crend().