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std::ranges::crbegin(3) C++ Standard Libary std::ranges::crbegin(3) NAME std::ranges::crbegin - std::ranges::crbegin Synopsis Defined in header <ranges> inline namespace /*unspecified*/ { inline constexpr /*unspecified*/ crbegin = (since C++20) /*unspecified*/; (customiza- tion point object) } Call signature template< class T > requires /* see below */ (since C++20) constexpr std::input_or_output_iterator auto crbegin( T&& t ); Returns an iterator to the first element of the const-qualified ar- gument 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::crbegin is expression-equivalent to ranges::rbegin(static_cast<CT&&>(t)). The return type models std::input_or_output_iterator in both cases. 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 poten- tially-throwing (i.e. noexcept(e) == noexcept(f)). Customization point objects The name ranges::crbegin 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 __crbegin_fn. All instances of __crbegin_fn are equal. The effects of invoking different instances of type __crbegin_fn on the same arguments are equivalent, regard- less 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::crbegin can be copied freely and its copies can be used in- terchangeably. Given a set of types Args..., if std::declval<Args>()... meet the requirements for arguments to ranges::crbegin above, __crbegin_fn models * std::invocable<__crbegin_fn, Args...>, * std::invocable<const __crbegin_fn, Args...>, * std::invocable<__crbegin_fn&, Args...>, and * std::invocable<const __crbegin_fn&, Args...>. Otherwise, no function call operator of __crbegin_fn participates in overload resolution. 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, the call to ranges::crbegin is ill-formed, which also results in substitution failure. The return type models std::input_or_output_iterator in all cases. Example // Run this code #include <iostream> #include <vector> #include <iterator> #include <span> int main() { std::vector<int> v = { 3, 1, 4 }; auto vi = std::ranges::crbegin(v); std::cout << *vi << '\n'; int a[] = { -5, 10, 15 }; auto ai = std::ranges::crbegin(a); std::cout << *ai << '\n'; // auto x_x = std::ranges::crbegin(std::vector<int>{6,6,6}); // ill-formed: the argument is an rvalue (see Notes ) auto si = std::ranges::crbegin(std::span{a}); // OK: static_assert(std::ranges::enable_borrowed_range< std::remove_cv_t<decltype(std::span{a})>>); std::cout << *si << '\n'; } Output: 4 15 15 See also ranges::rbegin returns a reverse iterator to a range (C++20) (customization point object) rbegin returns a reverse iterator to the beginning of a con- tainer or array crbegin (function template) (C++14) http://cppreference.com 2022.07.31 std::ranges::crbegin(3)
NAME | Synopsis | Notes | Example | Output: | See also
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