NAME¶

std::ranges::rend - std::ranges::rend

Synopsis¶

Defined in header <ranges>
Defined in header <iterator>
inline namespace /* unspecified */ {
(since C++20)
inline constexpr /* unspecified */ rend = /* unspecified (customization point
*/; object)

}
Call signature
template< class T >

requires /* see below */
constexpr std::sentinel_for< (since C++20)

decltype(ranges::rbegin(std::declval<T>()))> auto rend(
T&& t );

Returns a sentinel indicating the end of a reversed range.

range-rbegin-rend.svg

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.

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 removed such machinery
non-member rend found by ADL

See also¶

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