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Difference between revisions of "cpp/ranges/cend"

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< cpp‎ | ranges
m
(also available when <iterator> is included ([range.access.general]/1))
 
(4 intermediate revisions by 2 users not shown)
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{{dcl begin}}
 
{{dcl begin}}
 
{{dcl header|ranges}}
 
{{dcl header|ranges}}
 +
{{dcl header|iterator}}
 
{{dcl|notes={{mark custpt}}|since=c++20|1=
 
{{dcl|notes={{mark custpt}}|since=c++20|1=
 
inline namespace /* unspecified */ {
 
inline namespace /* unspecified */ {
Line 16: Line 17:
 
{{dcl end}}
 
{{dcl end}}
  
−
Returns a {{rev inl|since=c++23|constant}} sentinel indicating the end of a {{rev inl|until=c++23|const-qualified}} range.
+
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}}
  
−
{{rrev|until=c++23|
+
{{rrev multi|until1=c++23
 +
|rev1=
 
Let {{tt|CT}} be
 
Let {{tt|CT}} be
 
* {{c|const std::remove_reference_t<T>&}} if the argument is an lvalue (i.e. {{tt|T}} is an lvalue reference type),
 
* {{c|const std::remove_reference_t<T>&}} if the argument is an lvalue (i.e. {{tt|T}} is an lvalue reference type),
 
* {{c|const T}} otherwise.
 
* {{c|const T}} otherwise.
 
A call to {{tt|ranges::cend}} is [[cpp/language/expressions#Expression-equivalence|expression-equivalent]] to {{c|ranges::end(static_cast<CT&&>(t))}}.
 
A call to {{tt|ranges::cend}} is [[cpp/language/expressions#Expression-equivalence|expression-equivalent]] to {{c|ranges::end(static_cast<CT&&>(t))}}.
−
}}
+
|rev2=
−
 
+
−
{{rrev|since=c++23|
+
 
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:
 
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))}}.
 
* {{c|std::const_sentinel<decltype(U)>(U)}} for some expression {{tt|U}} equivalent to {{c|ranges::end(/*possibly-const-range*/(t))}}.
−
 
−
The function {{c|/*possibly-const-range*/(t)}} returns an lvalue [[cpp/language/expressions#Expression-equivalence|expression-equivalent]] to
 
−
* {{c|const_cast<const T&>(t)}}, if {{c|ranges::constant_range<const R> && !ranges::constant_range<R>}} is {{c|true}}.
 
−
* Otherwise, {{c|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.
 
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.
 
}}
 
}}
  
−
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 [[cpp/ranges/constant_range|<i>{{lc|constant-iterator}}</i>]] if it models {{lconcept|input_iterator}}.}}
+
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}}.}}
  
 
{{cpp/ranges/cpo}}
 
{{cpp/ranges/cpo}}
Line 47: Line 43:
 
|code=
 
|code=
 
#include <algorithm>
 
#include <algorithm>
−
#include <iostream>
+
#include <cassert>
 
#include <ranges>
 
#include <ranges>
 
#include <vector>
 
#include <vector>
Line 53: Line 49:
 
int main()
 
int main()
 
{
 
{
−
     std::vector<int> vec = {3, 1, 4};
+
     std::vector vec{3, 1, 4};
−
     int arr[] = {5, 10, 15};
+
     int arr[]{5, 10, 15};
  
−
     std::cout << std::boolalpha
+
     assert(std::ranges::find(vec, 5) == std::ranges::cend(vec));
−
              << "vec contains 5: "
+
    assert(std::ranges::find(arr, 5) != std::ranges::cend(arr));
−
              << (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
 
 
}}
 
}}
  

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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