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

Returns a sentinel indicating the end of a const-qualified range that is treated as a reversed sequence.


Let CT be.

  1. const std::remove_reference_t<T>& if the argument is a lvalue (i.e. T is an lvalue reference type),
  2. const T otherwise,

a call to ranges::crend is expression-equivalent to ranges::rend(static_cast<CT&&>(t)).

If ranges::crend(e) is valid for an expression e, then std::sentinel_for<S, I> is true in all cases, where S is decltype(ranges::crend(e)), and I is decltype(ranges::crbegin(e)).


Expression e is expression-equivalent to expression f, if.

  • e and f have the same effects, and
  • either both are constant subexpressions or else neither is a constant subexpression, and
  • either both are potentially-throwing or else neither is potentially-throwing (i.e. noexcept(e) == noexcept(f)).

Customization point objects

The name ranges::crend 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 __crend_fn.

All instances of __crend_fn are equal. The effects of invoking different instances of type __crend_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::crend 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::crend above, __crend_fn models

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


#include <iostream>
#include <vector>
#include <iterator>
#include <algorithm>
int main()
    int a[] = {4, 6, -3, 9, 10};
    std::cout << "Array backwards: ";
    namespace ranges = std::ranges;
    ranges::copy(ranges::rbegin(a), ranges::rend(a),
                 std::ostream_iterator<int>(std::cout, " "));
    std::cout << "\nVector backwards: ";
    std::vector<int> v = {4, 6, -3, 9, 10};
    ranges::copy(ranges::rbegin(v), ranges::rend(v),
                 std::ostream_iterator<int>(std::cout, " "));


Array backwards: 10 9 -3 6 4 
Vector backwards: 10 9 -3 6 4

See also

returns a reverse end iterator to a range
(customization point object)
returns a reverse end iterator for a container or array
(function template)

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