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

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

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
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)

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

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...>
• 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

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

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!

Defect reports

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

See also