operator-(std::reverse_iterator)

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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)
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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)

(C++20)

(C++20)

(C++26)

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)

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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)

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Defined in header`<iterator>`
template<class Iter1,class Iter2> typename reverse_iterator<Iter>::difference_type operator-(const reverse_iterator<Iter1>& lhs, const reverse_iterator<Iter2>& rhs);		(until C++11)
template<class Iter1,class Iter2> auto operator-(const reverse_iterator<Iter1>& lhs, const reverse_iterator<Iter2>& rhs) -> decltype(rhs.base()- lhs.base());		(since C++11) (constexpr since C++17)

Returns the distance between two iterator adaptors.

[edit]Parameters

lhs, rhs

iterator adaptors to compute the difference of

[edit]Return value

rhs.base()- lhs.base()

[edit]Notes

operator- returnsrhs.base()- lhs.base() rather thanlhs.base()- rhs.base() because this is a reverse iterator.

[edit]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)<<' ';// 4std::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 random access iterator}

Output:

4 -4

[edit]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 subtraction was not allowed	allowed

[edit]See also

operator++operator++(int)operator+=operator+operator--operator--(int)operator-=operator-	advances or decrements the`reverse_iterator` (public member function)[edit]
operator+	advances the iterator (function template)[edit]