Обратные итераторы (Reverse iterators)
Двунаправленные итераторы и итераторы произвольного доступа имеют соответствующие адаптеры обратных итераторов, которые выполняют итерации через структуру данных в противоположном направлении.Они имеют те же самые сигнатуры, как и соответствующие итераторы. Фундаментальное соотношение между обратным итератором и его соответствующим итератором i установлено тождеством &*(reverse_iterator(i)) == &*(i - 1). Это отображение продиктовано тем, что, в то время как после конца массива всегда есть указатель, может не быть допустимого указателя перед началом массива.
template <class BidirectionalIterator, class T, class Reference = T&, class Distance = ptrdiff_t> class reverse_bidirectionaiIterator : public bidirectional_iterator<T, Distance> { typedef reverse_bidirectional_iterator<BidirectionalIterator, T, Reference, Distance> self; friend bool operator==(const self& х, const self& y); protected: BidirectionalIterator current; public: reverse_bidirectional_iterator() {} reverse_bidirectional_iterator(BidirectionalIterator х) : current(х) {} BidirectionalIterator base() { return current; } Reference operator*() const { BidirectionalIterator tmp = current; return *--tmp; } self& operator++() { --current; return *this; } self operator++(int) { self tmp = *this; --current; return tmp; } self& operator--() { ++current; return *this; } self operator--(int) { self tmp = *this; ++current; return tmp; } }; template <class BidirectionalIterator, class T, class Reference, class Distance> inline bool operator==( const reverse_bidirectional_iterator<BidirectionalIterator, T, Reference, Distance>& x, const reverse_bidirectional_iterator<BidirectionalIterator, T, Reference, Distance>& y){ return x.current == y.current; } template <class RandomAccessIterator, class T, class Reference = T&, class Distance = ptrdiff_t> class reverse_iterator : public random_access_iterator<T, Distance>{ typedef reverse_iterator<RandomAccessIterator, T, Reference, Distance> self; friend bool operator==(const self& x, const self& y); friend bool operator<(const self& x, const self& y); friend Distance operator-(const self& x, const self& y); friend self operator+(Distance n, const self& x); protected: RandomAccessIterator current; public: reverse_iterator() {} reverse_iterator(RandomAccessIterator x) : current (x) {} RandomAccessIterator base() { return current; } Reference operator*() const { RandomAccessIterator tmp = current; return *--tmp; } self& operator++() { --current; return *this; } self operator++(int) { self tmp = *this; --current; return tmp; } self& operator--() { ++current; return *this; } self operator--(int) { self tmp = *this; ++current; return tmp; } self operator+(Distance n) const { return self (current - n); } self& operator+=(Distance n) { current -= n; return *this; } self operator-(Distance n) const { return self(current + n); } self operator-=(Distance n) { current +- n; return *this; } Reference operator[](Distance n) { return *(*this + n);} }; template <class RandomAccessIterator, class T, class Reference, class Distance> inline bool operator==( const reverse_iterator<RandomAccessIterator, T, Reference, Distance>& x, const reverse_iterator<RandomAccessIterator, T, Reference, Distance>& y) { return x.current == y.current; } template <class RandomAccessIterator, class T, class Reference, class Distance> inline bool operator<( const reverse_iterator<RandomAccessIterator, T, Reference, Distance>& x, const reverse_iterator<RandomAccessIterator, T, Reference, Distance>& y) { return y.current < x.current; } template <class RandomAccessIterator, class T, class Reference, class Distance> inline Distance operator-( const reverse_iterator<RandomAccessIterator, T, Reference, Distance>& х, const reverse_iterator<RandomAccessIterator, T, Reference, Distance>& y) { return y.current - x.current; } template <class RandomAccessIterator, class T, class Reference, class Distance> inline reverse_iterator<RandomAccessIterator, T, Reference, Distance> operator+( Distance n, const reverse_iterator<RandomAccessIterator, T, Reference, Distance>& x) { return reverse_iterator<RandomAccessIterator, T, Reference, Distance> (x.current - n); }