NAME¶

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

Synopsis¶

Defined in header <ranges>
Defined in header <iterator>
inline namespace /* unspecified */ {

inline constexpr /* unspecified */ crend = /* (since C++20)
unspecified */; (customization point object)

}
Call signature
template< class T >

requires /* see below */ (since C++20)

constexpr /* see below */ auto crend( T&& t );

Returns a sentinel
for the constant iterator
(since C++23) indicating the end of a
const-qualified
(until C++23) range that is treated as a reversed sequence.

range-rbegin-rend.svg

Let CT be

* const std::remove_reference_t<T>& if the argument is an lvalue (i.e. T is
an lvalue reference type), (until
* const T otherwise. C++23)

A call to ranges::crend is expression-equivalent to
ranges::rend(static_cast<CT&&>(t)).
If the argument is an lvalue or
ranges::enable_borrowed_range<std::remove_cv_t<T>> is true, then a call to
ranges::crend is expression-equivalent to:

* std::const_sentinel<decltype(U)>(U) for some expression U equivalent to (since
ranges::rend(/*possibly-const-range*/(t)). C++23)

In all other cases, a call to ranges::crend is ill-formed, which can result
in substitution failure when the call appears in the immediate context of a
template instantiation.

If ranges::crend(e) is valid for an expression e, where decltype((e)) is T, then
CT models std::ranges::range, and
(until C++23) std::sentinel_for<S, I> is true in all cases, where S is
decltype(ranges::crend(e)), and I is decltype(ranges::crbegin(e)).
Additionally, S models constant-iterator if it models input_iterator.
(since C++23)

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 <algorithm>
#include <iostream>
#include <iterator>
#include <vector>

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 << '\n';

std::cout << "Vector backwards: ";
std::vector v{4, 6, -3, 9, 10};
ranges::copy(ranges::rbegin(v), ranges::rend(v),
std::ostream_iterator<int>(std::cout, " "));
std::cout << '\n';
}

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)