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)

Diagnostics library

Memory management library

Metaprogramming library (C++11)

General utilities library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library (C++17)

Concurrency support library (C++11)

Execution control library (C++26)

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) is-integer-like is-signed-integer-like (C++20)(C++20)	sentinel_for (C++20) sized_sentinel_for (C++20) input_iterator (C++20) output_iterator (C++20) input_or_output_iterator (C++20)	forward_iterator (C++20) bidirectional_iterator (C++20) random_access_iterator (C++20) contiguous_iterator (C++20)
Iterator primitives
input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (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)	iterator (deprecated in C++17) iterator_traits incrementable_traits (C++20) indirectly_readable_traits (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)	projected_value_t (C++26)
Iterator adaptors
reverse_iterator make_reverse_iterator (C++14) move_iterator (C++11) make_move_iterator (C++11) default_sentinel_tdefault_sentinel (C++20)(C++20) unreachable_sentinel_tunreachable_sentinel (C++20)(C++20)	front_insert_iterator back_insert_iterator inserter insert_iterator front_inserter back_inserter 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) make_const_iterator (C++23) make_const_sentinel (C++23)
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) rbegincrbegin (C++14)(C++14)   endcend (C++11)(C++14) rendcrend (C++14)(C++14)   sizessize (C++17)(C++20) 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)

 

Defined in header <iterator>
template< class Iter1, class Iter2 > bool operator==( const std::reverse_iterator<Iter1>& lhs, const std::reverse_iterator<Iter2>& rhs );	(1)	(constexpr since C++17)
template< class Iter1, class Iter2 > bool operator!=( const std::reverse_iterator<Iter1>& lhs, const std::reverse_iterator<Iter2>& rhs );	(2)	(constexpr since C++17)
template< class Iter1, class Iter2 > bool operator< ( const std::reverse_iterator<Iter1>& lhs, const std::reverse_iterator<Iter2>& rhs );	(3)	(constexpr since C++17)
template< class Iter1, class Iter2 > bool operator<=( const std::reverse_iterator<Iter1>& lhs, const std::reverse_iterator<Iter2>& rhs );	(4)	(constexpr since C++17)
template< class Iter1, class Iter2 > bool operator> ( const std::reverse_iterator<Iter1>& lhs, const std::reverse_iterator<Iter2>& rhs );	(5)	(constexpr since C++17)
template< class Iter1, class Iter2 > bool operator>=( const std::reverse_iterator<Iter1>& lhs, const std::reverse_iterator<Iter2>& rhs );	(6)	(constexpr since C++17)
template< class Iter1, std::three_way_comparable_with<Iter1> Iter2 > constexpr std::compare_three_way_result_t<Iter1, Iter2> operator<=>( const std::reverse_iterator<Iter1>& lhs, const std::reverse_iterator<Iter2>& rhs );	(7)	(since C++20)

Compares the underlying iterators of lhs and rhs.

• The result of equality comparisons are preserved (i.e. equal underlying iterators imply equal reverse iterators).
• The result of relational comparisons are reversed (i.e. a greater underlying iterator implies a lesser reverse iterator).

1) This overload participates in overload resolution only if lhs.base() == rhs.base() is well-formed and convertible to bool. 2) This overload participates in overload resolution only if lhs.base() != rhs.base() is well-formed and convertible to bool. 3) This overload participates in overload resolution only if lhs.base() > rhs.base() is well-formed and convertible to bool. 4) This overload participates in overload resolution only if lhs.base() >= rhs.base() is well-formed and convertible to bool. 5) This overload participates in overload resolution only if lhs.base() < rhs.base() is well-formed and convertible to bool. 6) This overload participates in overload resolution only if lhs.base() <= rhs.base() is 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()

Notes

operator<=> returns rhs.base() <=> lhs.base() rather than lhs.base() <=> rhs.base() because this is a reverse iterator.

Example

Run this code

#include <cassert>
#include <iterator>

int main()
{
    int a[]{0, 1, 2, 3};
    //            ↑  └───── x, y
    //            └──────── z
    // “x” and “y” are equal, but “x” is less than “z” (reversely)
    std::reverse_iterator<int*>
        x{std::rend(a) - std::size(a)},
        y{std::rend(a) - std::size(a)},
        z{std::rbegin(a) + 1};

    // two-way comparisons
    assert(  x == y );
    assert(!(x != y));
    assert(!(x <  y));
    assert(  x <= y );
    assert(!(x == z));
    assert(  x != z );
    assert(  x <  z );
    assert(  x <= z );

    // three-way comparisons
    assert(  x <=> y == 0 );
    assert(!(x <=> y <  0));
    assert(!(x <=> y >  0));
    assert(!(x <=> z == 0));
    assert(  x <=> z <  0 );
    assert(!(x <=> z >  0));
}

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	heterogeneous assignment was not allowed	allowed