std::ranges::rend

 

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Ranges library (C++20)

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Ranges library

Range access begin cbegin   end cend rbegin crbegin   rend crend size ssize   data cdata empty

Range conversions std::from_range_t std::from_range (C++23)(C++23)     to (C++23)

Dangling iterator handling dangling borrowed_iterator_t borrowed_subrange_t

Range primitives
range_size_trange_difference_trange_value_t elements_of (C++23)	iterator_tconst_iterator_tsentinel_tconst_sentinel_t (C++23)(C++23)	range_reference_trange_const_reference_trange_rvalue_reference_trange_common_reference_t (C++23)

Range concepts
range borrowed_range    sized_range	common_range view viewable_range	input_range output_range forward_range	bidirectional_range    random_access_range contiguous_range	constant_range (C++23)

Views
view_interface	subrange

Range factories
empty_viewviews::empty	single_viewviews::single	basic_istream_viewviews::istream	iota_viewviews::iota	repeat_viewviews::repeat (C++23)(C++23)

Range adaptors
views::all_tviews::all ref_view owning_view as_rvalue_viewviews::as_rvalue (C++23)(C++23)   filter_viewviews::filter transform_viewviews::transform take_viewviews::take take_while_viewviews::take_while concat_viewviews::concat (C++26)(C++26)	drop_viewviews::drop drop_while_viewviews::drop_while join_viewviews::join join_with_viewviews::join_with (C++23)(C++23)   lazy_split_viewviews::lazy_split split_viewviews::split views::counted common_viewviews::common	reverse_viewviews::reverse as_const_viewviews::as_const (C++23)(C++23) elements_viewviews::elements keys_viewviews::keys values_viewviews::values enumerate_viewviews::enumerate (C++23)(C++23) zip_viewviews::zip (C++23)(C++23) zip_transform_viewviews::zip_transform (C++23)(C++23)	adjacent_viewviews::adjacent (C++23)(C++23) views::pairwise (C++23) adjacent_transform_viewviews::adjacent_transform (C++23)(C++23) views::pairwise_transform (C++23) chunk_viewviews::chunk (C++23)(C++23) slide_viewviews::slide (C++23)(C++23) chunk_by_viewviews::chunk_by (C++23)(C++23) stride_viewviews::stride (C++23)(C++23) cartesian_product_viewviews::cartesian_product (C++23)(C++23)

Range generators std::generator (C++23)

Range adaptor closure objects range_adaptor_closure (C++23)

Range adaptor objects

Helper items
copyable-box movable-box (until C++23)  (C++23)	simple-view non-propagating-cache

 

Defined in header <ranges>
Defined in header <iterator>
inline namespace /* unspecified */ {     inline constexpr /* unspecified */ rend = /* unspecified */; }		(since C++20) (customization point object)
Call signature
template< class T >     requires /* see below */ constexpr std::sentinel_for<     decltype(ranges::rbegin(std::declval<T>()))> auto rend( T&& t );		(since C++20)

Returns a sentinel indicating the end of a reversed range.

If T is an array type and std::remove_all_extents_t<std::remove_reference_t<T>> is incomplete, then the call to ranges::rend is ill-formed, no diagnostic required.

If the argument is an lvalue or ranges::enable_borrowed_range<std::remove_cv_t<T>> is true, then a call to ranges::rend is expression-equivalent to:

1. decay-copy(t.rend())(until C++23)auto(t.rend())(since C++23), if that expression is valid and its type models std::sentinel_for<decltype(ranges::rbegin(std::declval<T>()))>.
2. Otherwise, decay-copy(rend(t))(until C++23)auto(rend(t))(since C++23), if T is a class or enumeration type, that expression is valid and its type models std::sentinel_for<decltype(ranges::rbegin(std::declval<T>()))>, where the meaning of rend is established as if by performing argument-dependent lookup only.
3. Otherwise, std::make_reverse_iterator(ranges::begin(t)) if both ranges::begin(t) and ranges::end(t) are valid expressions, have the same type, and that type models std::bidirectional_iterator.

In all other cases, a call to ranges::rend is ill-formed, which can result in substitution failure when ranges::rend(t) appears in the immediate context of a template instantiation.

Customization point objects

The name ranges::rend denotes a customization point object, which is a const function object of a literal semiregular class type. For exposition purposes, the cv-unqualified version of its type is denoted as __rend_fn.

All instances of __rend_fn are equal. The effects of invoking different instances of type __rend_fn on the same arguments are equivalent, regardless of whether the expression denoting the instance is an lvalue or rvalue, and is const-qualified or not (however, a volatile-qualified instance is not required to be invocable). Thus, ranges::rend can be copied freely and its copies can be used interchangeably.

Given a set of types Args..., if std::declval<Args>()... meet the requirements for arguments to ranges::rend above, __rend_fn models

• std::invocable<__rend_fn, Args...>,
• std::invocable<const __rend_fn, Args...>,
• std::invocable<__rend_fn&, Args...>, and
• std::invocable<const __rend_fn&, Args...>.
  

Otherwise, no function call operator of __rend_fn participates in overload resolution.

Notes

If the argument is an rvalue (i.e. T is an object type) and ranges::enable_borrowed_range<std::remove_cv_t<T>> is false, or if it is of an array type of unknown bound, the call to ranges::rend is ill-formed, which also results in substitution failure.

If ranges::rend(std::forward<T>(t)) is valid, then decltype(ranges::rend(std::forward<T>(t))) and decltype(ranges::begin(std::forward<T>(t))) model std::sentinel_for in all cases, while T models std::ranges::range.

The C++20 standard requires that if the underlying rend function call returns a prvalue, the return value is move-constructed from the materialized temporary object. All implementations directly return the prvalue instead. The requirement is corrected by the post-C++20 proposal P0849R8 to match the implementations.

Example

Run this code

#include <algorithm>
#include <iostream>
#include <ranges>
#include <vector>
 
int main()
{
    std::vector<int> v = {3, 1, 4};
    namespace ranges = std::ranges;
    if (ranges::find(ranges::rbegin(v), ranges::rend(v), 5) != ranges::rend(v))
        std::cout << "found a 5 in vector v!\n";
 
    int a[] = {5, 10, 15};
    if (ranges::find(ranges::rbegin(a), ranges::rend(a), 5) != ranges::rend(a))
        std::cout << "found a 5 in array a!\n";
}

Output:

found a 5 in array a!

Defect reports

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

DR	Applied to	Behavior as published	Correct behavior
P2602R2	C++20	there's machinery to prohibit certain non-member rend found by ADL	removed such machinery

See also

ranges::crend (C++20)	returns a reverse end iterator to a read-only range (customization point object)
ranges::rbegin (C++20)	returns a reverse iterator to a range (customization point object)
rendcrend (C++14)	returns a reverse end iterator for a container or array (function template)