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Difference between revisions of "cpp/iterator/rend"

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< cpp‎ | iterator
m (Use since= and until= params of {{dcl}} template.)
m (→‎Synopsis: ~constexpr=)
 
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{{cpp/title| rend}}
+
{{cpp/title|rend|crend}}
 
{{cpp/iterator/navbar}}
 
{{cpp/iterator/navbar}}
 
{{dcl begin}}
 
{{dcl begin}}
−
{{dcl header | iterator}}
+
{{cpp/iterator/range access headers}}
−
{{dcl | num=1 | since=c++14 |
+
{{dcla|anchor=no|num=1|since=c++14|constexpr=c++17|
−
template< class C >  
+
template< class C >
 
auto rend( C& c ) -> decltype(c.rend());
 
auto rend( C& c ) -> decltype(c.rend());
 
}}
 
}}
−
{{dcl | num=1 | since=c++14 |
+
{{dcla|anchor=no|num=2|since=c++14|constexpr=c++17|
−
template< class C >  
+
template< class C >
 
auto rend( const C& c ) -> decltype(c.rend());
 
auto rend( const C& c ) -> decltype(c.rend());
 
}}
 
}}
−
{{dcl | num=2 | since=c++14 |
+
{{dcla|anchor=no|num=3|since=c++14|constexpr=c++17|
−
template< class T, size_t N >  
+
template< class T, std::size_t N >
−
T* rend( T (&array)[N] );
+
std::reverse_iterator<T*> rend( T (&array)[N] );
 
}}
 
}}
−
{{dcl | num=3 | since=c++14 |
+
{{dcla|anchor=no|num=4|since=c++14|constexpr=c++17|
−
template< class C >  
+
template< class T >
 +
std::reverse_iterator<const T*> rend( std::initializer_list<T> il );
 +
}}
 +
{{dcla|anchor=no|num=5|since=c++14|constexpr=c++17|
 +
template< class C >
 
auto crend( const C& c ) -> decltype(std::rend(c));
 
auto crend( const C& c ) -> decltype(std::rend(c));
 
}}
 
}}
 
{{dcl end}}
 
{{dcl end}}
  
−
Returns an iterator to the reverse-end of the given container {{tt|c}} or array {{tt|array}}.
+
Returns an iterator to the reverse-end of the given range.
  
−
@1@ Returns a possibly const-qualified iterator to the reverse-end of the container {{tt|c}}.
+
@1,2@ Returns {{c|c.rend()}}, which is typically an iterator one past the reverse-end of the sequence represented by {{c|c}}.
−
@2@ Returns a pointer to the reverse-end of the array {{tt|array}}.
+
:@1@ If {{tt|C}} is a standard {{named req|Container}}, returns a {{tt|C::reverse_iterator}} object.
−
@3@ Returns a const-qualified iterator to the reverse-end of the container {{tt|c}}.
+
:@2@ If {{tt|C}} is a standard {{named req|Container}}, returns a {{tt|C::const_reverse_iterator}} object.
 +
 
 +
@3@ Returns an {{c/core|std::reverse_iterator<T*>}} object to the reverse-end of {{c|array}}.
 +
 
 +
@4@ Returns an {{c/core|std::reverse_iterator<const T*>}} object to the reverse-end of {{c|il}}.
 +
 
 +
@5@ Returns {{c|std::end(c)}}, with {{c|c}} always treated as const-qualified.
 +
@@ If {{tt|C}} is a standard {{named req|Container}}, returns a {{tt|C::const_reverse_iterator}} object.
  
 
{{image|range-rbegin-rend.svg}}
 
{{image|range-rbegin-rend.svg}}
Line 31: Line 42:
 
===Parameters===
 
===Parameters===
 
{{par begin}}
 
{{par begin}}
−
{{par | c | a container with a {{tt|rend}} method}}
+
{{par|c|a container or view with a {{tt|rend}} member function}}
−
{{par | array | an array of arbitrary type}}
+
{{par|array|an array of arbitrary type}}
 +
{{par|il|an {{c/core|std::initializer_list}}}}
 
{{par end}}
 
{{par end}}
  
 
===Return value===
 
===Return value===
−
An iterator to the reverse-end of {{tt|c}} or {{tt|array}}
+
@1,2@ {{c|c.rend()}}
 +
@3@ {{c|std::reverse_iterator<T*>(array)}}
 +
@4@ {{c|std::reverse_iterator<const T*>(il.begin())}}
 +
@5@ {{c|c.rend()}}
  
−
===Notes===
+
{{cpp/impldef exception}}
−
In addition to being included in {{tt|<iterator>}}, {{tt|std::rend}} is guaranteed to become available if any of the following headers are included: {{tt|<array>}}, {{tt|<deque>}}, {{tt|<forward_list>}}, {{tt|<list>}}, {{tt|<map>}}, {{tt|<regex>}}, {{tt|<set>}}, {{tt|<string>}}, {{tt|<unordered_map>}}, {{tt|<unordered_set>}}, and {{tt|<vector>}}.
+
  
−
===Specializations===
+
===Overloads===
−
Custom specializations of {{tt|std::rend}} may be provided for classes that do not expose a suitable {{tt|rend()}} member function, yet can be iterated. The following specializations are already provided by the standard library:
+
Custom overloads of {{tt|rend}} may be provided for classes and enumerations that do not expose a suitable {{tt|rend()}} member function, yet can be iterated.
  
−
{{dsc begin}}
+
{{rrev|since=c++20|
−
{{dsc inc | cpp/utility/initializer_list/dsc rend2}}
+
Overloads of {{tt|rend}} found by [[cpp/language/adl|argument-dependent lookup]] can be used to customize the behavior of {{c/core|std::ranges::rend}} and {{lc|std::ranges::crend}}.
−
{{dsc inc | cpp/numeric/valarray/dsc rend2}}
+
}}
−
{{dsc end}}
+
 
 +
===Notes===
 +
The overload for {{lc|std::initializer_list}} is necessary because it does not have a member function {{tt|rend}}.
  
 
===Example===
 
===Example===
 
{{example
 
{{example
−
|
+
|code=
−
| code=
+
#include <algorithm>
−
| output=
+
#include <iostream>
 +
#include <iterator>
 +
#include <vector>
 +
 
 +
int main()
 +
{
 +
    int a[]{4, 6, -3, 9, 10};
 +
    std::cout << "C-style array `a` backwards: ";
 +
    std::copy(std::rbegin(a), std::rend(a), std::ostream_iterator<int>(std::cout, " "));
 +
   
 +
    auto il = {3, 1, 4};
 +
    std::cout << "\nstd::initializer_list `il` backwards: ";
 +
    std::copy(std::rbegin(il), std::rend(il), std::ostream_iterator<int>(std::cout, " "));
 +
   
 +
    std::vector<int> v{4, 6, -3, 9, 10};
 +
    std::cout << "\nstd::vector `v` backwards: ";
 +
    std::copy(std::rbegin(v), std::rend(v), std::ostream_iterator<int>(std::cout, " "));
 +
    std::cout << '\n';
 +
}
 +
|output=
 +
C-style array `a` backwards: 10 9 -3 6 4
 +
std::initializer_list `il` backwards: 4 1 3
 +
std::vector `v` backwards: 10 9 -3 6 4
 
}}
 
}}
  
 
===See also===
 
===See also===
 
{{dsc begin}}
 
{{dsc begin}}
−
{{dsc inc | cpp/iterator/dsc rbegin}}
+
{{dsc inc|cpp/iterator/dsc end}}
 +
{{dsc inc|cpp/iterator/dsc rbegin}}
 +
{{dsc inc|cpp/iterator/dsc begin}}
 +
{{dsc inc|cpp/ranges/dsc rend}}
 +
{{dsc inc|cpp/ranges/dsc crend}}
 
{{dsc end}}
 
{{dsc end}}
 +
 +
{{langlinks|es|ja|ru|zh}}

Latest revision as of 22:11, 1 November 2024

 
C++
 
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
Range access
(C++11)(C++14)
(C++14)(C++14)  
(C++11)(C++14)
rendcrend
(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 <inplace_vector>
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>
template< class C >
auto rend( C& c ) -> decltype(c.rend());
 (1) (since C++14)
(constexpr since C++17)
template< class C >
auto rend( const C& c ) -> decltype(c.rend());
 (2) (since C++14)
(constexpr since C++17)
template< class T, std::size_t N >
std::reverse_iterator<T*> rend( T (&array)[N] );
 (3) (since C++14)
(constexpr since C++17)
template< class T >
std::reverse_iterator<const T*> rend( std::initializer_list<T> il );
 (4) (since C++14)
(constexpr since C++17)
template< class C >
auto crend( const C& c ) -> decltype(std::rend(c));
 (5) (since C++14)
(constexpr since C++17)

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

1,2) Returns c.rend(), which is typically an iterator one past the reverse-end 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 an std::reverse_iterator<T*> object to the reverse-end of array.
4) Returns an std::reverse_iterator<const T*> object to the reverse-end of il.
5) Returns std::end(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 rend member function
array - an array of arbitrary type
il - an std::initializer_list

[edit] Return value

1,2) c.rend()
3) std::reverse_iterator<T*>(array)
4) std::reverse_iterator<const T*>(il.begin())
5) c.rend()

[edit] Exceptions

May throw implementation-defined exceptions.

[edit] Overloads

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

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

(since C++20)

[edit] Notes

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

[edit] Example

Run this code
#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>
 
int main()
{
    int a[]{4, 6, -3, 9, 10};
    std::cout << "C-style array `a` backwards: ";
    std::copy(std::rbegin(a), std::rend(a), std::ostream_iterator<int>(std::cout, " "));
 
    auto il = {3, 1, 4};
    std::cout << "\nstd::initializer_list `il` backwards: ";
    std::copy(std::rbegin(il), std::rend(il), std::ostream_iterator<int>(std::cout, " "));
 
    std::vector<int> v{4, 6, -3, 9, 10};
    std::cout << "\nstd::vector `v` backwards: ";
    std::copy(std::rbegin(v), std::rend(v), std::ostream_iterator<int>(std::cout, " "));
    std::cout << '\n';
}

Output: 

C-style array `a` backwards: 10 9 -3 6 4
std::initializer_list `il` backwards: 4 1 3
std::vector `v` backwards: 10 9 -3 6 4

[edit] See also

(C++11)(C++14)
 returns an iterator to the end of a container or array
(function template) [edit]
(C++14)
 returns a reverse iterator to the beginning of a container or array
(function template) [edit]
(C++11)(C++14)
 returns an iterator to the beginning of a container or array
(function template) [edit]
(C++20)
 returns a reverse end iterator to a range
(customization point object)[edit]
(C++20)
 returns a reverse end iterator to a read-only range
(customization point object)[edit]
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