< cpp‎ | ranges
Ranges library
Range access
Range conversions

Range primitives

Dangling iterator handling
Range concepts

Range factories
Range adaptors
Range generators
Range adaptor objects
Range adaptor closure objects
Helper items
(until C++23)(C++23)

Defined in header <ranges>
Defined in header <iterator>
inline namespace /* unspecified */ {

    inline constexpr /* unspecified */ rbegin = /* unspecified */;

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

    requires /* see below */

constexpr std::input_or_output_iterator auto rbegin( T&& t );
(since C++20)

Returns an iterator to the last element of the argument.


If T is an array type and std::remove_all_extents_t<std::remove_reference_t<T>> is incomplete, then the call to ranges::rbegin is ill-formed, no diagnostic required.

If the argument is an lvalue or ranges::enable_borrowed_range<std::remove_cv_t<T>> is true, then a call to ranges::rbegin is expression-equivalent to:

  1. decay-copy(t.rbegin())(until C++23)auto(t.rbegin())(since C++23), if that expression is valid and its type models std::input_or_output_iterator.
  2. Otherwise, decay-copy(rbegin(t))(until C++23)auto(rbegin(t))(since C++23), if T is a class or enumeration type, that expression is valid and its type models std::input_or_output_iterator, where the meaning of rbegin is established as if by performing argument-dependent lookup only.
  3. Otherwise, std::make_reverse_iterator(ranges::end(t)) if both ranges::begin(t) and ranges::end(t) are valid expressions, have the same type, and that type models std::bidirectional_iterator.

In all other cases, a call to ranges::rbegin is ill-formed, which can result in substitution failure when ranges::rbegin(t) appears in the immediate context of a template instantiation.


Customization point objects

The name ranges::rbegin 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 __rbegin_fn.

All instances of __rbegin_fn are equal. The effects of invoking different instances of type __rbegin_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::rbegin 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::rbegin above, __rbegin_fn models

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

[edit] Notes

If the argument is an rvalue (i.e. T is an object type) and ranges::enable_borrowed_range<std::remove_cv_t<T>> is false, the call to ranges::rbegin is ill-formed, which also results in substitution failure.

The return type models std::input_or_output_iterator in all cases.

The C++20 standard requires that if the underlying rbegin function call returns a prvalue, the return value is move-constructed from the materialized temporary object. All implementations directly return the prvalue instead. The requirement is corrected by the post-C++20 proposal P0849R8 to match the implementations.

[edit] Example

#include <iostream>
#include <ranges>
#include <span>
#include <vector>
int main()
    std::vector<int> v = {3, 1, 4};
    auto vi = std::ranges::rbegin(v);
    std::cout << *vi << '\n';
    *vi = 42; // OK
    int a[] = {-5, 10, 15};
    auto ai = std::ranges::rbegin(a);
    std::cout << *ai << '\n';
    *ai = 42; // OK
    // auto x_x = std::ranges::rbegin(std::vector{6, 6, 6});
    // ill-formed: the argument is an rvalue (see Notes ↑)
    auto si = std::ranges::rbegin(std::span{a}); // OK
    *si = 42; // OK



[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
P2602R2 C++20 there's machinery to prohibit certain non-member rbegin found by ADL removed such machinery

[edit] See also

returns a reverse iterator to a read-only range
(customization point object)[edit]
returns a reverse iterator to the beginning of a container or array
(function template) [edit]