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Difference between revisions of "cpp/ranges/cend"

From cppreference.com
< cpp‎ | ranges
m (→‎Synopsis: () => ( ))
(also available when <iterator> is included ([range.access.general]/1))
 
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{{cpp/ranges/title | cend}}
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{{cpp/ranges/title|cend}}
 
{{cpp/ranges/navbar}}
 
{{cpp/ranges/navbar}}
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{{dcl begin}}
 
{{dcl begin}}
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{{dcl header|ranges}}
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{{dcl header | ranges}}
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{{dcl header|iterator}}
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{{dcl|notes={{mark custpt}}|since=c++20|1=
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{{dcl | notes={{mark custpt}} | since=c++20 | 1=
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inline namespace /* unspecified */ {
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inline namespace /*unspecified*/ {
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     inline constexpr /* unspecified */ cend = /* unspecified */;
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     inline constexpr /*unspecified*/ cend = /*unspecified*/;
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}
 
}
 
}}
 
}}
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{{dcl h|Call signature}}
 
{{dcl h|Call signature}}
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{{dcl | since=c++20 |1=
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{{dcl|since=c++20|1=
 
template< class T >
 
template< class T >
 
     requires /* see below */
 
     requires /* see below */
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constexpr std::sentinel_for<ranges::iterator_t<T>> auto cend( T&& t );
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constexpr /* see below */ auto cend( T&& t );
 
}}
 
}}
 
{{dcl end}}
 
{{dcl end}}
  
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Returns a sentinel indicating the end of a const-qualified range.
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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.
  
 
{{image|range-begin-end.svg}}
 
{{image|range-begin-end.svg}}
  
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{{rrev multi|until1=c++23
 +
|rev1=
 
Let {{tt|CT}} be
 
Let {{tt|CT}} be
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# {{c|const std::remove_reference_t<T>&}} if the argument is a lvalue (i.e. {{tt|T}} is an lvalue reference type),
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* {{c|const std::remove_reference_t<T>&}} if the argument is an lvalue (i.e. {{tt|T}} is an lvalue reference type),
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# {{c|const T}} otherwise,
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* {{c|const T}} otherwise.
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a call to {{tt|ranges::cend}} is expression-equivalent to {{c|ranges::end(static_cast<CT&&>(t))}}.
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A call to {{tt|ranges::cend}} is [[cpp/language/expressions#Expression-equivalence|expression-equivalent]] to {{c|ranges::end(static_cast<CT&&>(t))}}.
 +
|rev2=
 +
If the argument is an lvalue or {{c|ranges::enable_borrowed_range<std::remove_cv_t<T>>}} is {{c|true}}, then a call to {{tt|ranges::cend}} is [[cpp/language/expressions#Expression-equivalence|expression-equivalent]] to:
 +
* {{c|std::const_sentinel<decltype(U)>(U)}} for some expression {{tt|U}} equivalent to {{c|ranges::end(/*possibly-const-range*/(t))}}.
 +
 
 +
In all other cases, a call to {{tt|ranges::cend}} is ill-formed, which can result in [[cpp/language/sfinae|substitution failure]] when the call appears in the immediate context of a template instantiation.
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}}
  
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If {{c|ranges::cend(e)}} is valid for an expression {{c|e}}, where {{c|decltype((e))}} is {{tt|T}}, then {{tt|CT}} models {{lc|std::ranges::range}}, and {{c|std::sentinel_for<S, I>}} is {{c|true}} in all cases, where {{tt|S}} is {{c|decltype(ranges::cend(e))}}, and {{tt|I}} is {{c|decltype(ranges::cbegin(e))}}.
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If {{c|ranges::cend(e)}} is valid for an expression {{c|e}}, where {{c|decltype((e))}} is {{tt|T}}, then {{rev inl|until=c++23|{{tt|CT}} models {{lc|std::ranges::range}}, and}} {{c|std::sentinel_for<S, I>}} is {{c|true}} in all cases, where {{tt|S}} is {{c|decltype(ranges::cend(e))}}, and {{tt|I}} is {{c|decltype(ranges::cbegin(e))}}. {{rev inl|since=c++23|Additionally, {{tt|S}} models {{rlpi|constant_range|constant-iterator}} if it models {{lconcept|input_iterator}}.}}
  
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{{cpp/expr-eq}}
 
 
{{cpp/ranges/cpo}}
 
{{cpp/ranges/cpo}}
  
 
===Example===
 
===Example===
 
{{example
 
{{example
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|
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|
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| code=
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|code=
 
#include <algorithm>
 
#include <algorithm>
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#include <iostream>
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#include <cassert>
 
#include <ranges>
 
#include <ranges>
 
#include <vector>
 
#include <vector>
  
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int main()  
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int main()
 
{
 
{
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     std::vector<int> v = { 3, 1, 4 };
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     std::vector vec{3, 1, 4};
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     namespace ranges = std::ranges;
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     int arr[]{5, 10, 15};
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    if (ranges::find(v, 5) != ranges::cend(v)) {
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        std::cout << "found a 5 in vector v!\n";
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−
    }
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     int a[] = { 5, 10, 15 };
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     assert(std::ranges::find(vec, 5) == std::ranges::cend(vec));
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    if (ranges::find(a, 5) != ranges::cend(a)) {
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    assert(std::ranges::find(arr, 5) != std::ranges::cend(arr));
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        std::cout << "found a 5 in array a!\n";
+
−
    }
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}
 
}
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| output=found a 5 in array a!
 
 
}}
 
}}
  
 
===See also===
 
===See also===
 
{{dsc begin}}
 
{{dsc begin}}
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{{dsc inc | cpp/ranges/dsc end}}
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{{dsc inc|cpp/ranges/dsc end}}
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{{dsc inc | cpp/iterator/dsc end}}
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{{dsc inc|cpp/iterator/dsc end}}
 
{{dsc end}}
 
{{dsc end}}
  
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{{langlinks|es|ja|zh}}
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{{langlinks|de|es|ja|ru|zh}}

Latest revision as of 09:29, 8 September 2023

 
C++
 
Ranges library
Range adaptors
 
Defined in header <ranges>
Defined in header <iterator>
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.

range-begin-end.svg

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:

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

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

[edit] 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));
}

[edit] See also

(C++20)
 returns a sentinel indicating the end of a range
(customization point object)[edit]
(C++11)(C++14)
 returns an iterator to the end of a container or array
(function template) [edit]
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