Difference between revisions of "cpp/ranges/cend"
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| − | Returns a {{rev inl|since=c++23|constant}} | + | Returns a sentinel{{rev inl|since=c++23| for the constant iterator}} indicating the end of a {{rev inl|until=c++23|const-qualified}} range. |
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Revision as of 22:28, 30 July 2023
| Defined in header <ranges>
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| inline namespace /* unspecified */ { inline constexpr /* unspecified */ cend = /* unspecified */; |
(since C++20) (customization point object) |
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| Call signature |
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| template< class T > requires /* see below */ |
(since C++20) | |
Returns a sentinel for the constant iterator(since C++23) indicating the end of a const-qualified(until C++23) range.
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Let
A call to |
(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
The function /*possibly-const-range*/(t) returns an lvalue expression-equivalent to
In all other cases, a call to |
(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
#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'; }
Output:
vec contains 5: false arr contains 5: true
See also
| (C++20) |
returns a sentinel indicating the end of a range (customization point object) |
| (C++11)(C++14) |
returns an iterator to the end of a container or array (function template) |
