Difference between revisions of "cpp/ranges/cend"

Revision as of 07:14, 30 July 2023

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

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

#include <algorithm>
#include <iostream>
#include <ranges>
#include <vector>
 
int main()
{
    std::vector<int> vec = {3, 1, 4};
    int arr[] = {5, 10, 15};
 
    std::cout << std::boolalpha
              << "vec contains 5: "
              << (std::ranges::find(vec, 5) != std::ranges::cend(vec)) << '\n'
              << "arr contains 5: "
              << (std::ranges::find(arr, 5) != std::ranges::cend(arr)) << '\n';
}

vec contains 5: false
arr contains 5: true

See also