std::ranges::views::take, std::ranges::take_view

< cpp‎ | ranges
Defined in header <ranges>
template< ranges::view V >
class take_view : public ranges::view_interface<take_view<V>>
(1) (since C++20)
namespace views {

    inline constexpr /*unspecified*/ take = /*unspecified*/;

(2) (since C++20)
1) A range adaptor that represents view of the first N elements from an underlying sequence, or all elements if the underlying sequence contains fewer than N.
2) The expression views::take(E, F) results in a view that represents the first F elements from E. The result is not necessarily a take_view.

It is expression-equivalent to (where T is std::remove_cvref_t<decltype((E))> and D is ranges::range_difference_t<decltype((E))>):

  • std::span where T::extent == std::dynamic_extent,
  • std::basic_string_view,
  • ranges::iota_view, or
  • ranges::subrange;
  • otherwise, take_view{E, F}.

In all cases, decltype((F)) must model std::convertible_to<D>.


[edit] Expression-equivalent

Expression e is expression-equivalent to expression f, if e and f have the same effects, either are both potentially-throwing or are both not potentially-throwing (i.e. noexcept(e) == noexcept(f)), and either are both constant subexpressions or are both not constant subexpressions.

[edit] Member functions

constructs a take_view
(public member function) [edit]
returns a copy of the underlying (adapted) view
(public member function) [edit]
returns an iterator to the beginning
(public member function) [edit]
returns an iterator or a sentinel to the end
(public member function) [edit]
returns the number of elements. Provided only if the underlying (adapted) range satisfies sized_range
(public member function) [edit]

[edit] Deduction guides

[edit] Nested classes

the sentinel type
(public member class)

[edit] Helper templates

template<class T>

inline constexpr bool enable_borrowed_range<std::ranges::take_view<T>> =

(since C++20)

This specialization of std::ranges::enable_borrowed_range makes take_view satisfy borrowed_range when the underlying view satisfies it.

[edit] Example

#include <algorithm>
#include <iostream>
#include <ranges>
auto print = [](char x) { std::cout << x; };
int main()
    constexpr char pi[] { '3', '.', '1', '4', '1', '5', '9', '2' };
    std::ranges::for_each(pi | std::ranges::views::take(6), print);
    std::cout << '\n';
    std::ranges::for_each(std::ranges::take_view{pi, 42}, print); // safely takes only 8 chars
    std::cout << '\n';



[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 3494 C++20 take_view was never a borrowed_range it is a borrowed_range if its underlying view is

[edit] See also

creates a subrange from an iterator and a count
(customization point object) [edit]
a view consisting of the initial elements of another view, until the first element on which a predicate returns false
(class template) (range adaptor object) [edit]
copies a number of elements to a new location
(niebloid) [edit]