std::ranges::rend(3) C++ Standard Libary std::ranges::rend(3) NAME std::ranges::rend - std::ranges::rend Synopsis Defined in header <ranges> Defined in header <iterator> inline namespace /* unspecified */ { (since C++20) inline constexpr /* unspecified */ rend = /* unspecified (cus- tomization point */; object) } Call signature template< class T > requires /* see below */ constexpr std::sentinel_for< (since C++20) decltype(ranges::rbegin(std::declval<T>()))> auto rend( T&& t ); Returns a sentinel indicating the end of a reversed range. range-rbegin-rend.svg If T is an array type and std::remove_all_extents_t<std::remove_refer- ence_t<T>> is incomplete, then the call to ranges::rend is ill-formed, no diagnostic required. If the argument is an lvalue or ranges::enable_borrowed_range<std::re- move_cv_t<T>> is true, then a call to ranges::rend is expression-equivalent to: 1. decay-copy(t.rend()) (until C++23) auto(t.rend()) (since C++23), if that expression is valid and its type models std::sentinel_for<decltype(ranges::rbegin(std::declval<T>()))>. 2. Otherwise, decay-copy(rend(t)) (until C++23) auto(rend(t)) (since C++23), if T is a class or enumeration type, that expression is valid and its type models std::sentinel_for<decltype(ranges::rbegin(std::de- clval<T>()))>, where the meaning of rend is established as if by performing argu- ment-dependent lookup only. 3. Otherwise, std::make_reverse_iterator(ranges::begin(t)) if both ranges::begin(t) and ranges::end(t) are valid expressions, have the same type, and that type models std::bidirectional_iterator. In all other cases, a call to ranges::rend is ill-formed, which can re- sult in substitution failure when ranges::rend(t) appears in the immediate con- text of a template instantiation. Notes If the argument is an rvalue (i.e. T is an object type) and ranges::enable_borrowed_range<std::remove_cv_t<T>> is false, or if it is of an array type of unknown bound, the call to ranges::rend is ill-formed, which also results in substitution failure. If ranges::rend(std::forward<T>(t)) is valid, then decltype(ranges::rend(std::forward<T>(t))) and decltype(ranges::begin(std::forward<T>(t))) model std::sentinel_for in all cases, while T models std::ranges::range. The C++20 standard requires that if the underlying rend function call returns a prvalue, the return value is move-constructed from the materialized tem- porary object. All implementations directly return the prvalue instead. The re- quirement is corrected by the post-C++20 proposal P0849R8 to match the implementa- tions. Example // Run this code #include <algorithm> #include <iostream> #include <ranges> #include <vector> int main() { std::vector<int> v = {3, 1, 4}; namespace ranges = std::ranges; if (ranges::find(ranges::rbegin(v), ranges::rend(v), 5) != ranges::rend(v)) std::cout << "found a 5 in vector v!\n"; int a[] = {5, 10, 15}; if (ranges::find(ranges::rbegin(a), ranges::rend(a), 5) != ranges::rend(a)) std::cout << "found a 5 in array a!\n"; } Output: found a 5 in array a! Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct behavior P2602R2 C++20 there's machinery to prohibit certain removed such machinery non-member rend found by ADL See also ranges::crend returns a reverse end iterator to a read-only range (C++20) (customization point object) ranges::rbegin returns a reverse 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::rend(3)
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