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std::rbegin, std::crbegin

From cppreference.com
< cpp‎ | iterator
 
 
Iterator library
Iterator concepts
Iterator primitives
Algorithm concepts and utilities
Indirect callable concepts
Common algorithm requirements
(C++20)
(C++20)
(C++20)
Utilities
(C++20)
Iterator adaptors
Iterator customization points
Iterator operations
(C++11)    
(C++11)
Range access
(C++11)(C++14)
rbegincrbegin
(C++14)(C++14)    
(C++11)(C++14)
(C++14)(C++14)    
(C++17)(C++20)
(C++17)
(C++17)
 
Defined in header <array>
Defined in header <deque>
Defined in header <flat_map>
Defined in header <flat_set>
Defined in header <forward_list>
Defined in header <iterator>
Defined in header <list>
Defined in header <map>
Defined in header <regex>
Defined in header <set>
Defined in header <span>
Defined in header <string>
Defined in header <string_view>
Defined in header <unordered_map>
Defined in header <unordered_set>
Defined in header <vector>
(1)
template< class C >
auto rbegin( C& c ) -> decltype(c.rbegin());
(since C++14)
(until C++17)
template< class C >
constexpr auto rbegin( C& c ) -> decltype(c.rbegin());
(since C++17)
(2)
template< class C >
auto rbegin( const C& c ) -> decltype(c.rbegin());
(since C++14)
(until C++17)
template< class C >
constexpr auto rbegin( const C& c ) -> decltype(c.rbegin());
(since C++17)
(3)
template< class T, std::size_t N >
std::reverse_iterator<T*> rbegin( T (&array)[N] );
(since C++14)
(until C++17)
template< class T, std::size_t N >
constexpr std::reverse_iterator<T*> rbegin( T (&array)[N] );
(since C++17)
(4)
template< class T >
std::reverse_iterator<const T*> rbegin( std::initializer_list<T> il );
(since C++14)
(until C++17)
template< class T >

constexpr std::reverse_iterator<const T*>

    rbegin( std::initializer_list<T> il );
(since C++17)
(5)
template< class C >
auto crbegin( const C& c ) -> decltype(std::rbegin(c));
(since C++14)
(until C++17)
template< class C >
constexpr auto crbegin( const C& c ) -> decltype(std::rbegin(c));
(since C++17)

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

1,2) Returns c.begin(), which is typically an iterator to the 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<const T*> 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.

range-rbegin-rend.svg

Contents

[edit] Parameters

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

[edit] Return value

1,2) c.rbegin()
3) std::reverse_iterator<T*>(array + N)
4) std::reverse_iterator<const T*>(il.end())
5) c.rbegin()

[edit] Exceptions

May throw implementation-defined exceptions.

[edit] 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)

[edit] Notes

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

[edit] 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

[edit] See also

(C++11)(C++14)
returns an iterator to the beginning of a container or array
(function template) [edit]
(C++11)(C++14)
returns an iterator to the end of a container or array
(function template) [edit]
(C++14)
returns a reverse end iterator for a container or array
(function template) [edit]
returns a reverse iterator to a range
(customization point object)[edit]
returns a reverse iterator to a read-only range
(customization point object)[edit]