# std::ranges::cend

From cppreference.com
< cpp‎ | ranges

Defined in header `<ranges>` |  |
inline namespace /* unspecified */ { inline constexpr /* unspecified */ cend = /* unspecified */; } |  | (since C++20) (customization point object)
Call signature |  |
template< class T > requires /* see below */ constexpr /* see below */ auto cend( T&& t ); |  | (since C++20)

Returns a sentinel for the constant iterator (since C++23) indicating the end of a const-qualified (until C++23) range.

Let `CT` be const std::remove_reference_t<T>& if the argument is an lvalue (i.e. `T` is an lvalue reference type), const T otherwise. A call to `ranges::cend` is expression-equivalent to ranges::end(static_cast<CT&&>(t)). | (until C++23)
If the argument is an lvalue or ranges::enable_borrowed_range<std::remove_cv_t<T>> is true, then a call to `ranges::cend` is expression-equivalent to: std::const_sentinel<decltype(U)>(U) for some expression `U` equivalent to ranges::end(/*possibly-const-range*/(t)). In all other cases, a call to `ranges::cend` is ill-formed, which can result in substitution failure when the call appears in the immediate context of a template instantiation. | (since C++23)

If ranges::cend(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::cend(e)), and `I` is decltype(ranges::cbegin(e)). Additionally, `S` models `constant-iterator` if it models `input_iterator`. (since C++23)

### Customization point objects

The name `ranges::cend` 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 `__cend_fn`.

All instances of `__cend_fn` are equal. The effects of invoking different instances of type `__cend_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::cend` 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::cend` above, `__cend_fn` models

- std::invocable<__cend_fn, Args...>,
- std::invocable<const __cend_fn, Args...>,
- std::invocable<__cend_fn&, Args...>, and
- std::invocable<const __cend_fn&, Args...>.

Otherwise, no function call operator of `__cend_fn` participates in overload resolution.

### Example

Run this code

    #include <algorithm>
    #include <cassert>
    #include <ranges>
    #include <vector>

    int main()
    {
        std::vector vec{3, 1, 4};
        int arr[]{5, 10, 15};

        assert(std::ranges::find(vec, 5) == std::ranges::cend(vec));
        assert(std::ranges::find(arr, 5) != std::ranges::cend(arr));
    }

### See also

ranges::end (C++20) | returns a sentinel indicating the end of a range (customization point object)
end cend (C++11)(C++14) | returns an iterator to the end of a container or array (function template)

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/ranges/cend&oldid=156220"