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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> Defined in header <iterator> 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 /* see below */ auto crbegin( T&& t ); Returns an iterator to the first element of the const-qualified (until C++23) argument that is treated as a reversed sequence. Returns a constant iterator to the first element of the argument that (since C++23) 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::crbegin is expression-equivalent to ranges::rbegin(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::crbegin is expression-equivalent to: * std::const_iterator<decltype(U)>(U) for some expression U equiv- alent to (since ranges::rbegin(/*possibly-const-range*/(t)). C++23) In all other cases, a call to ranges::crbegin is ill-formed, which can result in substitution failure when the call appears in the immediate con- text of a template instantiation. The return type models std::input_or_output_iterator and constant-iterator (since C++23) in all cases. 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. Example // Run this code #include <cassert> #include <iterator> #include <span> #include <vector> int main() { std::vector<int> v{3, 1, 4}; auto vi = std::ranges::crbegin(v); assert(*vi == 4); ++vi; // OK, iterator object is mutable assert(*vi == 1); // *vi = 13; // Error: underlying element is read-only int a[]{-5, 10, 15}; auto ai = std::ranges::crbegin(a); assert(*ai == 15); // 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 assert(*si == 15); static_assert ( std::ranges::enable_borrowed_range<std::remove_cv_t<de- cltype(std::span{a})>> ); } 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 2024.06.10 std::ranges::crbegin(3)
NAME | Synopsis | Example | See also
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