std::rbegin, std::crbegin

Defined in header `<array>`
Defined in header `<deque>`
Defined in header `<flat_map>`		(since C++23)
Defined in header `<flat_set>`		(since C++23)
Defined in header `<forward_list>`
Defined in header `<hive>`		(since C++26)
Defined in header `<inplace_vector>`		(since C++26)
Defined in header `<iterator>`
Defined in header `<list>`
Defined in header `<map>`
Defined in header `<optional>`		(since C++26)
Defined in header `<regex>`
Defined in header `<set>`
Defined in header `<span>`		(since C++20)
Defined in header `<stacktrace>`		(since C++23)
Defined in header `<string>`
Defined in header `<string_view>`		(since C++17)
Defined in header `<unordered_map>`
Defined in header `<unordered_set>`
Defined in header `<valarray>`
Defined in header `<vector>`

template< class C > auto rbegin( C& c ) noexcept(noexcept(c.rbegin())) -> decltype(c.rbegin());	(1)	(since C++14) (constexpr since C++17)
template< class C > auto rbegin( const C& c ) noexcept(noexcept(c.rbegin())) -> decltype(c.rbegin());	(2)	(since C++14) (constexpr since C++17)
template< class T, std::size_t N > std::reverse_iterator<T*> rbegin( T (&array)[N] ) noexcept;	(3)	(since C++14) (constexpr since C++17)
template< class T > std::reverse_iterator<const T*> rbegin( std::initializer_list<T> il ) noexcept;	(4)	(since C++14) (constexpr since C++17)
template< class C > auto crbegin( const C& c ) noexcept(noexcept(std::rbegin(c))) -> decltype(std::rbegin(c));	(5)	(since C++14) (constexpr since C++17)

Returns an iterator to the reverse-beginning of the given range.

1,2) Returns c.rbegin(), which is typically an iterator to the reverse-beginning of the sequence represented by c.

1) If C is a standard Container, returns a C::reverse_iterator object.

2) If C is a standard Container, returns a C::const_reverse_iterator object.

3) Returns a std::reverse_iterator<T*> object to the reverse-beginning of array.

4) Returns a std::reverse_iterator<constT*> object to the reverse-beginning of il.

5) Returns std::rbegin(c), with c always treated as const-qualified.

If C is a standard Container, returns a C::const_reverse_iterator object.

Parameters

c	-	a container or view with a `rbegin` member function
array	-	an array of arbitrary type
il	-	an std::initializer_list

Return value

1,2) c.rbegin()

3) std::reverse_iterator<T*>(array + N)

4) std::reverse_iterator<const T*>(il.end())

5) std::rbegin(c)

Exceptions

1,2) What and when underlying c.rbegin() call throws.

5) What and when underlying std::rbegin(c) call throws.

Overloads

Custom overloads of rbegin may be provided for classes and enumerations that do not expose a suitable rbegin() member function, yet can be iterated.

Overloads of rbegin found by argument-dependent lookup can be used to customize the behavior of std::ranges::rbegin and std::ranges::crbegin.

(since C++20)

Notes

The overload for std::initializer_list is necessary because it does not have a member function rbegin.

Example

#include <iostream>
#include <iterator>
#include <vector>

int main()
{
    std::vector<int> v = {3, 1, 4};
    auto vi = std::rbegin(v); // the type of “vi” is std::vector<int>::reverse_iterator
    std::cout << "*vi = " << *vi << '\n';
    
    *std::rbegin(v) = 42; // OK: after assignment v[2] == 42
//  *std::crbegin(v) = 13; // error: the location is read-only
    
    int a[] = {-5, 10, 15};
    auto ai = std::rbegin(a); // the type of “ai” is std::reverse_iterator<int*>
    std::cout << "*ai = " << *ai << '\n';
    
    auto il = {3, 1, 4};
    // the type of “it” below is std::reverse_iterator<int const*>:
    for (auto it = std::rbegin(il); it != std::rend(il); ++it)
        std::cout << *it << ' ';
    std::cout << '\n';
}

Output:

*vi = 4
*ai = 15
4 1 3

Defect reports

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

DR	Applied to	Behavior as published	Correct behavior
LWG 3537	C++14	`std::rbegin` and `std::crbegin` were not required to propagate exception specification	required

begincbegin (C++11)(C++14)	returns an iterator to the beginning of a container or array (function template)
endcend (C++11)(C++14)	returns an iterator to the end of a container or array (function template)
rendcrend (C++14)	returns a reverse end iterator for a container or array (function template)
ranges::rbegin (C++20)	returns a reverse iterator to a range (customization point object)
ranges::crbegin (C++20)	returns a reverse iterator to a read-only range (customization point object)