std::ranges::views::take, std::ranges::take_view - cppreference.com (original) (raw)

1. A range adaptor that represents view of the elements from an underlying sequence, starting at the beginning and ending at a given bound.

2. views::take is a RangeAdaptorObject. 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.

views::take(e, f) is expression-equivalent to (where T is std::remove_cvref_t<decltype((e))> and D is ranges::range_difference_t<decltype((e))>):

• ((void)f, decay-copy(e)), if T is a ranges::empty_view, except that the evaluations of e and f are indeterminately sequenced;

• U(ranges::begin(e), ranges::begin(e) + std::min<D>(ranges::distance(e), f)), if T is a specialization of std::span, std::basic_string_view, or ranges::subrange that models both random_access_range and sized_range, where U is

• std::span<typename T::element_type>, if T is a specialization of std::span;

• T, if T is a specialization of std::basic_string_view;

• ranges::subrange<ranges::iterator_t<T>>, if T is a specialization of ranges::subrange;

• ranges::iota_view(*ranges::begin(e),
  *(ranges::begin(e) + std::min<D>(ranges::distance(e), f))), if T is a specialization of ranges::iota_view that models both random_access_range and sized_range;

• otherwise, take_view(e, f).

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

take_view models the concepts contiguous_range, random_access_range, bidirectional_range, forward_range, input_range, and sized_range when the underlying view V models respective concepts. It models common_range when the underlying view V models both random_access_range and sized_range.

Contents

• 1 Data members
• 2 Member functions
  • 2.1 Inherited from std::ranges::view_interface
• 3 Deduction guides
• 4 Nested classes
• 5 Helper templates
• 6 Example
• 7 Defect reports
• 8 See also

[edit] Data members

[edit] Member functions

[edit] Deduction guides

[edit] Nested classes

| | the sentinel type(exposition-only member class template*) | | ------------------------------------------------------------- |

[edit] Helper templates

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

[edit] Example

#include #include #include   int main() { namespace views = std::views; auto print = [](char x){ std::cout << x; };   for (const char nums[]{'1', '2', '3'}; int n : views::iota(0, 5)) { std::cout << "take(" << n << "): "; // safely takes only upto min(n, nums.size()) elements: std::ranges::for_each(nums | views::take(n), print); std::cout << '\n'; } }

Output:

take(0): take(1): 1 take(2): 12 take(3): 123 take(4): 123

[edit] Defect reports

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

[edit] See also