std::ranges:: views:: join, std::ranges:: join_view

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_range and common_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_range and common_range .

Member functions

Deduction guides

Nested classes

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
}

Example

#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';
}

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Defect reports

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

See also