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

Non-member begin() and end() or C++11 iterator range accrss. Sven Johannsen 14.08.2014 C++ User Group Aachen. Always use nonmember begin(x) and end(x).

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

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  1. Non-member begin() and end()or C++11 iterator range accrss Sven Johannsen14.08.2014 C++ User Group Aachen

  2. 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 Sutter Elements of Modern C++ Style

  3. 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()); …

  4. 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.” Boost Range / Overview

  5. 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 Range non 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

  6. Non Member begin() and end() Unified iterator access for any container Addition 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).

  7. Non-Member for Non-STL Container E.g.: Range based for loop for non STL containers template<class T> CArrayIterator<T> begin(constCArray<T>& arr); template<class T> CArrayIterator<T> end(constCArray<T>& arr); ... CArray<int> arr; ... for(inti : arr) { cout << i << " " << endl; } bool sorted = std::is_sorted(begin(arr), end(arr));

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

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