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std::ranges::crend

From cppreference.com
< cpp‎ | ranges
 
 
 
Defined in header <ranges>
inline namespace /*unspecified*/ {

    inline constexpr /*unspecified*/ crend = /*unspecified*/;

}
(since C++20)
(customization point object)
Call signature
template< class T >

    requires /* see below */

constexpr std::sentinel_for<ranges::iterator_t<T>> auto crend(T&& t);

Returns a sentinel indicating the end of a const-qualified range that is treated as a reversed sequence.

range-rbegin-rend.svg

Let CT be

  1. const std::remove_reference_t<T>& if the argument is a lvalue (i.e. T is an lvalue reference type),
  2. const T otherwise,

a call to ranges::crend is expression-equivalent to ranges::rend(static_cast<CT&&>(t)).

If ranges::crend(e) is valid for an expression e, then std::sentinel_for<S, I> is true in all cases, where S is decltype(ranges::crend(e)), and I is decltype(ranges::crbegin(e)).

Contents

[edit] Expression-equivalent

Expression e is expression-equivalent to expression f, if e and f have the same effects, either are both potentially-throwing or are both not potentially-throwing (i.e. noexcept(e) == noexcept(f)), and either are both constant subexpressions or are both not constant subexpressions.

[edit] Customization point objects

The name ranges::crend denotes a customization point object, which is a const function object of a literal semiregular class type (denoted, for exposition purposes, as crend_ftor). All instances of crend_ftor are equal. Thus, ranges::crend 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::crend above, crend_ftor will satisfy std::invocable<const crend_ftor&, Args...>. Otherwise, no function call operator of crend_ftor participates in overload resolution.

[edit] Example

#include <iostream>
#include <vector>
#include <iterator>
#include <algorithm>
 
int main()
{
    int a[] = {4, 6, -3, 9, 10};
    std::cout << "Array backwards: ";
    namespace ranges = std::ranges;
    ranges::copy(ranges::rbegin(a), ranges::rend(a),
                 std::ostream_iterator<int>(std::cout, " "));
 
    std::cout << "\nVector backwards: ";
    std::vector<int> v = {4, 6, -3, 9, 10};
    ranges::copy(ranges::rbegin(v), ranges::rend(v),
                 std::ostream_iterator<int>(std::cout, " "));
}

Output:

Array backwards: 10 9 -3 6 4 
Vector backwards: 10 9 -3 6 4

[edit] See also

returns a reverse end iterator to a range
(customization point object) [edit]
(C++14)
returns a reverse end iterator for a container or array
(function template) [edit]