std::ranges::crend
| Defined in header <ranges>
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| Defined in header <iterator>
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| inline namespace /* unspecified */ { inline constexpr /* unspecified */ crend = /* unspecified */; |
(since C++20) (customization point object) |
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| Call signature |
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| template< class T > requires /* see below */ |
(since C++20) | |
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.
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Let
A call to |
(until C++23) |
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If the argument is an lvalue or ranges::enable_borrowed_range<std::remove_cv_t<T>> is true, then a call to
In all other cases, a call to |
(since C++23) |
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
#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
| (C++20) |
returns a reverse end iterator to a range (customization point object) |
| (C++14) |
returns a reverse end iterator for a container or array (function template) |