std::ranges:: crend

Returns a sentinel for the constant iterator (since C++23) indicating the end of a const-qualified (until C++23) range that is treated as a reversed sequence.

If ranges :: crend ( 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 :: crend ( e ) ) , and I is decltype ( ranges:: crbegin ( e ) ) . Additionally, S models constant-iterator if it models input_iterator . (since C++23)

Customization point objects

The name ranges::crend 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 __crend_fn .

All instances of __crend_fn are equal. The effects of invoking different instances of type __crend_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::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_fn models

• std:: invocable < __crend_fn, Args... > ,
• std:: invocable < const __crend_fn, Args... > ,
• std:: invocable < __crend_fn & , Args... > , and
• std:: invocable < const __crend_fn & , Args... > .
  

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

Example

#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>
 
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 << '\n';
 
    std::cout << "Vector backwards: ";
    std::vector v{4, 6, -3, 9, 10};
    ranges::copy(ranges::rbegin(v), ranges::rend(v),
                 std::ostream_iterator<int>(std::cout, " "));
    std::cout << '\n';
}

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

See also