operator==,!=,<,<=,>,>=,<=>(std::reverse_iterator)

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Iterator library

Iterator concepts
indirectly_readable (C++20) indirectly_writable (C++20) weakly_incrementable (C++20) incrementable (C++20) input_or_output_iterator (C++20) sentinel_for (C++20) sized_sentinel_for (C++20)	input_iterator (C++20) output_iterator (C++20) forward_iterator (C++20) bidirectional_iterator (C++20) random_access_iterator (C++20) contiguous_iterator (C++20)
Iterator primitives
iterator_traits input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20) iterator (deprecated in C++17)	incrementable_traits (C++20) indirectly_readable_traits (C++20) iter_value_titer_difference_titer_reference_titer_const_reference_titer_rvalue_reference_titer_common_reference_t (C++20)(C++20)(C++20)(C++23)(C++20)(C++20)
Algorithm concepts and utilities
Indirect callable concepts
indirectly_unary_invocableindirectly_regular_unary_invocable (C++20)(C++20)   indirect_unary_predicate (C++20)	indirect_binary_predicate (C++20) indirect_equivalence_relation (C++20) indirect_strict_weak_order (C++20)
Common algorithm requirements
indirectly_movable (C++20) indirectly_movable_storable (C++20) indirectly_copyable (C++20) indirectly_copyable_storable (C++20)	indirectly_swappable (C++20) indirectly_comparable (C++20) permutable (C++20) mergeable (C++20) sortable (C++20)
Utilities
indirect_result_t (C++20)	projected (C++20)
Iterator adaptors
reverse_iterator move_iterator (C++11) move_sentinel (C++20) common_iterator (C++20) counted_iterator (C++20) basic_const_iterator (C++23) const_iterator (C++23) const_sentinel (C++23) back_insert_iterator front_insert_iterator insert_iterator	make_reverse_iterator (C++14) make_move_iterator (C++11) default_sentinel_tdefault_sentinel (C++20)(C++20) unreachable_sentinel_tunreachable_sentinel (C++20)(C++20) make_const_iterator (C++23) make_const_sentinel (C++23) back_inserter front_inserter inserter
Stream iterators
istream_iterator ostream_iterator	istreambuf_iterator ostreambuf_iterator
Iterator customization points
ranges::iter_move (C++20)
ranges::iter_swap (C++20)
Iterator operations
advance distance prev (C++11) next (C++11)	ranges::advance (C++20) ranges::distance (C++20) ranges::prev (C++20) ranges::next (C++20)
Range access
begincbegin (C++11)(C++14) endcend (C++11)(C++14) sizessize (C++17)(C++20)	rbegincrbegin (C++14)(C++14) rendcrend (C++14)(C++14) empty (C++17) data (C++17)

 

std::reverse_iterator

Member functions

reverse_iterator::reverse_iterator

reverse_iterator::operator=

reverse_iterator::base

reverse_iterator::operator*reverse_iterator::operator->

reverse_iterator::operator[]

reverse_iterator::operator++reverse_iterator::operator+reverse_iterator::operator+=reverse_iterator::operator--reverse_iterator::operator-reverse_iterator::operator-=

Non-member functions

operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20)

operator+

operator-

iter_move (C++20)

iter_swap (C++20)

make_reverse_iterator (C++14)

 

	(1)
template< class Iterator1, class Iterator2 > bool operator==( const std::reverse_iterator<Iterator1>& lhs,                  const std::reverse_iterator<Iterator2>& rhs );			(until C++17)
template< class Iterator1, class Iterator2 > constexpr bool operator==( const std::reverse_iterator<Iterator1>& lhs,                            const std::reverse_iterator<Iterator2>& rhs );			(since C++17)
		(2)
template< class Iterator1, class Iterator2 > bool operator!=( const std::reverse_iterator<Iterator1>& lhs,                  const std::reverse_iterator<Iterator2>& rhs );				(until C++17)
template< class Iterator1, class Iterator2 > constexpr bool operator!=( const std::reverse_iterator<Iterator1>& lhs,                            const std::reverse_iterator<Iterator2>& rhs );				(since C++17)
			(3)
template< class Iterator1, class Iterator2 > bool operator<( const std::reverse_iterator<Iterator1>& lhs,                 const std::reverse_iterator<Iterator2>& rhs );					(until C++17)
template< class Iterator1, class Iterator2 > constexpr bool operator<( const std::reverse_iterator<Iterator1>& lhs,                           const std::reverse_iterator<Iterator2>& rhs );					(since C++17)
				(4)
template< class Iterator1, class Iterator2 > bool operator<=( const std::reverse_iterator<Iterator1>& lhs,                  const std::reverse_iterator<Iterator2>& rhs );						(until C++17)
template< class Iterator1, class Iterator2 > constexpr bool operator<=( const std::reverse_iterator<Iterator1>& lhs,                            const std::reverse_iterator<Iterator2>& rhs );						(since C++17)
					(5)
template< class Iterator1, class Iterator2 > bool operator>( const std::reverse_iterator<Iterator1>& lhs,                 const std::reverse_iterator<Iterator2>& rhs );							(until C++17)
template< class Iterator1, class Iterator2 > constexpr bool operator>( const std::reverse_iterator<Iterator1>& lhs,                           const std::reverse_iterator<Iterator2>& rhs );							(since C++17)
						(6)
template< class Iterator1, class Iterator2 > bool operator>=( const std::reverse_iterator<Iterator1>& lhs,                  const std::reverse_iterator<Iterator2>& rhs );								(until C++17)
template< class Iterator1, class Iterator2 > constexpr bool operator>=( const std::reverse_iterator<Iterator1>& lhs,                            const std::reverse_iterator<Iterator2>& rhs );								(since C++17)
template< class Iterator1, std::three_way_comparable_with<Iterator1> Iterator2 > constexpr std::compare_three_way_result_t<Iterator1, Iterator2>     operator<=>( const std::reverse_iterator<Iterator1>& lhs,                  const std::reverse_iterator<Iterator2>& rhs );							(7)	(since C++20)

Compares the underlying iterators. Inverse comparisons are applied in order to take into account that the iterator order is reversed.

(1-6) only participate in overload resolution if their underlying comparison expressions (see below) are well-formed and convertible to bool.

(since C++20)

Parameters

lhs, rhs

-

iterator adaptors to compare

Return Value

1) lhs.base() == rhs.base()

2) lhs.base() != rhs.base()

3) lhs.base() > rhs.base()

4) lhs.base() >= rhs.base()

5) lhs.base() < rhs.base()

6) lhs.base() <= rhs.base()

7) rhs.base() <=> lhs.base()

Example

Run this code

#include <compare>
#include <iostream>
#include <iterator>
 
int main()
{
    int a[]{0, 1, 2, 3};
    //            ↑  └───── x, y
    //            └──────── z
 
    std::reverse_iterator<int*>
        x {std::rend(a) - std::size(a)},
        y {std::rend(a) - std::size(a)},
        z {std::rbegin(a) + 1};
 
    std::cout
        << std::boolalpha
        << "*x == " << *x << '\n' // 3
        << "*y == " << *y << '\n' // 3
        << "*z == " << *z << '\n' // 2
        << "x == y ? " << (x == y) << '\n' // true
        << "x != y ? " << (x != y) << '\n' // false
        << "x <  y ? " << (x <  y) << '\n' // false
        << "x <= y ? " << (x <= y) << '\n' // true
        << "x == z ? " << (x == z) << '\n' // false
        << "x != z ? " << (x != z) << '\n' // true
        << "x <  z ? " << (x <  z) << '\n' // true
        << "x <= z ? " << (x <= z) << '\n' // true
        << "x <=> y == 0 ? " << (x <=> y == 0) << '\n' // true
        << "x <=> y <  0 ? " << (x <=> y <  0) << '\n' // false
        << "x <=> y >  0 ? " << (x <=> y >  0) << '\n' // false
        << "x <=> z == 0 ? " << (x <=> z == 0) << '\n' // false
        << "x <=> z <  0 ? " << (x <=> z <  0) << '\n' // true
        << "x <=> z >  0 ? " << (x <=> z >  0) << '\n' // false
        ;
}

Output:

*x == 3
*y == 3
*z == 2
x == y ? true
x != y ? false
x <  y ? false
x <= y ? false
x == z ? false
x != z ? true
x <  z ? true
x <= z ? true
x <=> y == 0 ? true
x <=> y <  0 ? false
x <=> y >  0 ? false
x <=> z == 0 ? false
x <=> z <  0 ? true
x <=> z >  0 ? false

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 280	C++98	an std::reverse_iterator could only compare with another std::reverse_iterator with the same underlying iterator type	allowed comparisons of std::reverse_iterator with different underlying iterator types