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Class template reverse_iterator is an iterator adaptor that iterates from the end of the sequence defined by its underlying iterator to the beginning of that sequence.

24.5.1.2 Class template reverse_iterator [reverse.iterator]

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namespace std { template<class Iterator> class reverse_iterator { public: using iterator_type = Iterator; using iterator_concept = see below; using iterator_category = see below; using value_type = iter_value_t<Iterator>; using difference_type = iter_difference_t<Iterator>; using pointer = iterator_traits<Iterator>::pointer; using reference = iter_reference_t<Iterator>; constexpr reverse_iterator(); constexpr explicit reverse_iterator(Iterator x); template<class U> constexpr reverse_iterator(const reverse_iterator<U>& u); template<class U> constexpr reverse_iterator& operator=(const reverse_iterator<U>& u); constexpr Iterator base() const; constexpr reference operator*() const; constexpr pointer operator->() const requires see below; constexpr reverse_iterator& operator+(); constexpr reverse_iterator operator+(int); constexpr reverse_iterator& operator-(); constexpr reverse_iterator operator-(int); constexpr reverse_iterator operator+ (difference_type n) const; constexpr reverse_iterator& operator+=(difference_type n); constexpr reverse_iterator operator- (difference_type n) const; constexpr reverse_iterator& operator-=(difference_type n); constexpr unspecified operator[](difference_type n) const; friend constexpr iter_rvalue_reference_t<Iterator> iter_move(const reverse_iterator& i) noexcept(see below); template<indirectly_swappable<Iterator> Iterator2> friend constexpr void iter_swap(const reverse_iterator& x, const reverse_iterator<Iterator2>& y) noexcept(see below); protected: Iterator current; }; }
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The member typedef-name iterator_concept denotes
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The member typedef-name iterator_category denotes
  • (2.1)
    random_access_iterator_tag if the type iterator_traits<​Iterator>​::​iterator_category models derived_from<random_access_iterator_tag>, and
  • (2.2)
    iterator_traits<​Iterator>​::​iterator_category otherwise.
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The template parameter Iterator shall either meet the requirements of a Cpp17BidirectionalIterator ([bidirectional.iterators]) or model bidirectional_iterator ([iterator.concept.bidir]).
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Additionally, Iterator shall either meet the requirements of a Cpp17RandomAccessIterator ([random.access.iterators]) or model random_access_iterator ([iterator.concept.random.access]) if the definitions of any of the members or the non-member operators ([reverse.iter.cmp]) are instantiated ([temp.inst]).

24.5.1.4 Construction and assignment [reverse.iter.cons]

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constexpr reverse_iterator();
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Effects: Value-initializes current.
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constexpr explicit reverse_iterator(Iterator x);
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Effects: Initializes current with x.
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template<class U> constexpr reverse_iterator(const reverse_iterator<U>& u);
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Constraints: is_same_v<U, Iterator> is false and const U& models convertible_to<Iterator>.
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Effects: Initializes current with u.current.
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template<class U> constexpr reverse_iterator& operator=(const reverse_iterator<U>& u);
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Constraints: is_same_v<U, Iterator> is false, const U& models convertible_to<Iterator>, and assignable_from<Iterator&, const U&> is modeled.
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Returns: *this.
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constexpr Iterator base() const;
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Returns: current.
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constexpr reference operator*() const;
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Effects: As if by: Iterator tmp = current; return *-tmp;
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constexpr pointer operator->() const requires (is_pointer_v<Iterator> || requires(const Iterator i) { i.operator->(); });
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Effects:
  • (2.1)
    If Iterator is a pointer type, equivalent to: return prev(current);
  • (2.2)
    Otherwise, equivalent to: return prev(current).operator->();
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constexpr unspecified operator[](difference_type n) const;
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Returns: current[-n - 1].
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constexpr reverse_iterator operator+(difference_type n) const;
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Returns: reverse_iterator(current - n).
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constexpr reverse_iterator operator-(difference_type n) const;
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Returns: reverse_iterator(current + n).
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constexpr reverse_iterator& operator+();
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Returns: *this.
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constexpr reverse_iterator operator+(int);
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Effects: As if by: reverse_iterator tmp = *this; --current; return tmp;
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constexpr reverse_iterator& operator-();
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Returns: *this.
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constexpr reverse_iterator operator-(int);
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Effects: As if by: reverse_iterator tmp = *this; ++current; return tmp;
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constexpr reverse_iterator& operator+=(difference_type n);
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Returns: *this.
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constexpr reverse_iterator& operator-=(difference_type n);
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Returns: *this.
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template<class Iterator1, class Iterator2> constexpr bool operator=( const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y);
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Constraints: x.base() == y.base() is well-formed and convertible to bool.
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Returns: x.base() == y.base().
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template<class Iterator1, class Iterator2> constexpr bool operator!=( const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y);
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Constraints: x.base() != y.base() is well-formed and convertible to bool.
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Returns: x.base() != y.base().
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template<class Iterator1, class Iterator2> constexpr bool operator<( const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y);
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Constraints: x.base() > y.base() is well-formed and convertible to bool.
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Returns: x.base() > y.base().
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template<class Iterator1, class Iterator2> constexpr bool operator>( const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y);
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Constraints: x.base() < y.base() is well-formed and convertible to bool.
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Returns: x.base() < y.base().
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template<class Iterator1, class Iterator2> constexpr bool operator<=( const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y);
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Constraints: x.base() >= y.base() is well-formed and convertible to bool.
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Returns: x.base() >= y.base().
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template<class Iterator1, class Iterator2> constexpr bool operator>=( const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y);
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Constraints: x.base() <= y.base() is well-formed and convertible to bool.
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Returns: x.base() <= y.base().
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template<class Iterator1, three_way_comparable_with<Iterator1> Iterator2> constexpr compare_three_way_result_t<Iterator1, Iterator2> operator<=>(const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y);
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[Note 1: 
The argument order in the Returns: element is reversed because this is a reverse iterator.
— end note]

24.5.1.9 Non-member functions [reverse.iter.nonmember]

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template<class Iterator1, class Iterator2> constexpr auto operator-( const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y) -> decltype(y.base() - x.base();
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Returns: y.base() - x.base().
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template<class Iterator> constexpr reverse_iterator<Iterator> operator+( iter_difference_t<Iterator> n, const reverse_iterator<Iterator>& x);
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Returns: reverse_iterator<Iterator>(x.base() - n).
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friend constexpr iter_rvalue_reference_t<Iterator> iter_move(const reverse_iterator& i) noexcept(see below);
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Effects: Equivalent to: auto tmp = i.base(); return ranges::iter_move(-tmp);
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Remarks: The exception specification is equivalent to: is_nothrow_copy_constructible_v<Iterator> && noexcept(ranges::iter_move(-declval<Iterator&>()
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template<indirectly_swappable<Iterator> Iterator2> friend constexpr void iter_swap(const reverse_iterator& x, const reverse_iterator<Iterator2>& y) noexcept(see below);
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Effects: Equivalent to: auto xtmp = x.base(); auto ytmp = y.base(); ranges::iter_swap(-xtmp, --ytmp);
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Remarks: The exception specification is equivalent to: is_nothrow_copy_constructible_v<Iterator> && is_nothrow_copy_constructible_v<Iterator2> && noexcept(ranges::iter_swap(-declval<Iterator&>(), --declval<Iterator2&>()
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template<class Iterator> constexpr reverse_iterator<Iterator> make_reverse_iterator(Iterator i);
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Returns: reverse_iterator<Iterator>(i).

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