std::reverse_iterator<Iter>::operator[]

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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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/* unspecified */ operator[]( difference_type n)const;		(constexpr since C++17)

Returns a reference to the element at specified relative location.

[edit]Parameters

position relative to current location

[edit]Return value

current[-n-1]

[edit]Notes

The return type was changed byLWG issue 386 to be unspecified because the return type of the underlying iterator'soperator[] was also unspecified at the time.

However, as ofN3066, the return type of aLegacyRandomAccessIterator'soperator[] is required to be convertible toreference. In all common implementations, the return type is declared to bereference. See alsoLWG issue 2595.

[edit]Example

Run this code

#include <array>#include <cstddef>#include <iostream>#include <iterator>#include <list>#include <vector> int main(){int a[]{0,1,2,3};std::reverse_iterator<int*> iter1{std::rbegin(a)};for(std::size_t i{}; i!=std::size(a);++i)std::cout<< iter1[i]<<' ';// decltype(iter1[i]) is int&std::cout<<'\n'; std::vector v{0,1,2,3};std::reverse_iterator<std::vector<int>::iterator> iter2{std::rbegin(v)};for(std::size_t i{}; i!=std::size(v);++i)std::cout<< iter2[i]<<' ';// decltype(iter2[i]) is int&std::cout<<'\n'; // constexpr contextconstexprstaticstd::array<int,4> z{0,1,2,3};constexprstd::reverse_iterator<decltype(z)::const_iterator> iter3{std::crbegin(z)};    static_assert(iter3[1]==2); std::list li{0,1,2,3};std::reverse_iterator<std::list<int>::iterator> iter4{std::rbegin(li)};*iter4=42;// OK//  iter4[0] = 13; // Compilation error: the underlying iterator// does not model the random access iterator}