std::ranges::crend(3)

NAME
std::ranges::crend - std::ranges::crend

Synopsis
   Defined in header <ranges>
   inline namespace /*unspecified*/ {
                        (since C++20)
   inline constexpr /*unspecified*/ crend = /*unspecified*/; (customization point
                        object)
   }
   Call signature
   template< class T >
   requires /* see below */ (since C++20)
   constexpr std::sentinel_for<ranges::iterator_t<T>> auto crend(
   T&& t );
   Returns a sentinel indicating the end of a const-qualified range that is treated as
   a reversed sequence.
   range-rbegin-rend.svg
   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-equivalent
   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
     * std::invocable<__crend_fn, Args...>,
     * std::invocable<const __crend_fn, Args...>,
     * std::invocable<__crend_fn&, Args...>, and
     * std::invocable<const __crend_fn&, Args...>.
   Otherwise, no function call operator of __crend_fn participates in overload
   resolution.

Example
// Run this code
 #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, " "));
 }

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

See also
   ranges::rend returns a reverse end 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)