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)