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)

 

template< class Iterator1, class Iterator2 > typename reverse_iterator<Iterator1>::difference_type     operator-( const reverse_iterator<Iterator1>& lhs,                const reverse_iterator<Iterator2>& rhs );		(until C++11)
template< class Iterator1, class Iterator2 > auto operator-( const reverse_iterator<Iterator1>& lhs,                 const reverse_iterator<Iterator2>& rhs               ) -> decltype(rhs.base() - lhs.base());		(since C++11) (until C++17)
template< class Iterator1, class Iterator2 > constexpr auto operator-( const reverse_iterator<Iterator1>& lhs,                           const reverse_iterator<Iterator2>& rhs                         ) -> decltype(rhs.base() - lhs.base());		(since C++17)

Returns the distance between two iterator adaptors.

Parameters

lhs, rhs

-

iterator adaptors to compute the difference of

Return value

rhs.base() - lhs.base()

Example

Run this code

#include <iostream>
#include <iterator>
#include <list>
#include <vector>
 
int main()
{
    std::vector vec{0, 1, 2, 3};
    std::reverse_iterator<std::vector<int>::iterator>
        vec_ri1{std::reverse_iterator{vec.rbegin()}},
        vec_ri2{std::reverse_iterator{vec.rend()}};
    std::cout << (vec_ri2 - vec_ri1) << ' '; // 4
    std::cout << (vec_ri1 - vec_ri2) << '\n'; // -4
 
    std::list lst{5, 6, 7, 8};
    std::reverse_iterator<std::list<int>::iterator>
        lst_ri1{std::reverse_iterator{lst.rbegin()}},
        lst_ri2{std::reverse_iterator{lst.rend()}};
//  auto n = (lst_ri1 - lst_ri2); // error: the underlying iterators do not
                                  // model the random access iterators
}

Output:

4 -4

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	subtrction between std::reverse_iterator with different underlying iterator types was not allowed	allowed

See also

operator++operator++(int)operator+=operator+operator--operator--(int)operator-=operator-	advances or decrements the iterator (public member function)
operator+	advances the iterator (function template)