std::ranges::crend(3) | C++ Standard Libary | 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)
2022.07.31 | http://cppreference.com |