std::ranges::rend

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. See CustomizationPointObject for details.

[edit] 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.

[edit] Example

#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";
}

found a 5 in array a!

[edit] Defect reports

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

[edit] See also