std::ranges::views::join, std::ranges::join_view
From cppreference.com
C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Ranges library
(public member function of
returns a sentinel for the constant iterator of the range
(public member function of
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++26)(C++26)
join_viewviews::join
(C++23)(C++23)
(C++26)(C++26)
(C++26)(C++26)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)
(C++23)(C++23)
(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)
std::ranges::join_view
Defined in header
<ranges>
template< ranges::input_range V >
(1)
(since C++20)
requires ranges::view <V> and
ranges::input_range <ranges::range_reference_t <V>>
class join_view
namespace views {
(2)
(since C++20)
inline constexpr /* unspecified */ join = /* unspecified */;
Call signature
template< ranges::viewable_range R >
(since C++20)
requires /* see below */
1) A range adaptor that represents
view consisting of the sequence obtained from flattening a view of ranges.2) RangeAdaptorObject (and also RangeAdaptorClosureObject). The expression views::join(e) is expression-equivalent to join_view<views::all_t <decltype((e))>>{e} for any suitable subexpressions e.
join_view models input_range.
join_view models forward_range when:
- ranges::range_reference_t <V> is a reference type, and
- V and ranges::range_reference_t <V> each model
forward_range.
join_view models bidirectional_range when:
- ranges::range_reference_t <V> is a reference type,
- V models
bidirectional_range, and - ranges::range_reference_t <V> models both
bidirectional_rangeandcommon_range.
join_view models common_range when:
- ranges::range_reference_t <V> is a reference type, and
- V and ranges::range_reference_t <V> each model
forward_rangeandcommon_range.
Contents
[edit] Member functions
Inherited from std::ranges::view_interface
returns whether the derived view is empty, provided only if it satisfies
(public member function of
sized_range or forward_range (public member function of
std::ranges::view_interface<D>) [edit]
(C++23)
(public member function of
std::ranges::view_interface<D>) [edit]
(C++23)
(public member function of
std::ranges::view_interface<D>) [edit]
returns whether the derived view is not empty, provided only if ranges::empty is applicable to it
(public member function of
(public member function of
std::ranges::view_interface<D>) [edit]
returns the first element in the derived view, provided if it satisfies
(public member function of
forward_range (public member function of
std::ranges::view_interface<D>) [edit]
returns the last element in the derived view, provided only if it satisfies
(public member function of
bidirectional_range and common_range (public member function of
std::ranges::view_interface<D>) [edit]
[edit] Deduction guides
[edit] Nested classes
[edit] Notes
Before P2328R1 was adopted, the inner range type (ranges::range_reference_t <V>) cannot be a container type (but can be reference to container). For example, it was not allowed to join a transform_view of std::string prvalue.
struct Person { int age; std::string name; }; auto f(std::vector <Person>& v) { // return v | std::views::transform([](auto& p){ return p.name; }) // | std::views::join; // error before P2328R1 return v | std::views::transform ([](auto& p) -> std::string & { return p.name; }) | std::views::join; // OK }
[edit] Example
Run this code
#include <iostream> #include <ranges> #include <string_view> #include <vector> int main() { using namespace std::literals; const auto bits = {"https:"sv, "//"sv, "cppreference"sv, "."sv, "com"sv}; for (char const c : bits | std::views::join) std::cout << c; std::cout << '\n'; const std::vector <std::vector <int>> v{{1, 2}, {3, 4, 5}, {6}, {7, 8, 9}}; auto jv = std::ranges::join_view(v); for (int const e : jv) std::cout << e << ' '; std::cout << '\n'; }
Output:
https://cppreference.com 1 2 3 4 5 6 7 8 9
[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 |
|---|---|---|---|
| LWG 3474 | C++20 | views::join(e) returned a copy of e when e is a join_view
|
returns a nested join_view
|
| P2328R1 | C++20 | non-view range prvalues could not be joined by join_view
|
made joinable |
[edit] See also
a
(class template) (range adaptor object)[edit]
view consisting of the sequence obtained from flattening a view of ranges, with the delimiter in between elements(class template) (range adaptor object)[edit]