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std::ranges::crend(3) C++ Standard Libary std::ranges::crend(3) 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 */; (customiza- tion 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 equiv- alent 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 con- text of a template instantiation. If ranges::crend(e) is valid for an expression e, where de- cltype((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_itera- tor. (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 dif- ferent 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 inter- changeably. 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) http://cppreference.com 2024.06.10 std::ranges::crend(3)
NAME | Synopsis | Example | Output: | See also
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