std::ranges::views::filter, std::ranges::filter_view - cppreference.com (original) (raw)

1. A range adaptor that represents view of an underlying sequence with only the elements that satisfy the predicate.

filter_view models the concepts bidirectional_range, forward_range, input_range, and common_range when the underlying view V models respective concepts.

Contents

• 1 Data members
• 2 Member functions
  • 2.1 Inherited from std::ranges::view_interface
• 3 std::ranges::filter_view::filter_view
  • 3.1 Parameters
• 4 std::ranges::filter_view::base
• 5 std::ranges::filter_view::pred
• 6 std::ranges::filter_view::begin
• 7 std::ranges::filter_view::end
  • 7.1 Deduction guides
  • 7.2 Nested classes
  • 7.3 Example
  • 7.4 Defect reports
  • 7.5 See also

[edit] Data members

[edit] Member functions

std::ranges::filter_view::filter_view

1. Value-initializes _base_ via its default member initializer (= V()) and default-initializes _pred_ (which value-initializes the contained Pred).

2. Initializes _base_ with std::move(base) and initializes _pred_ with std::move(pred).

Parameters

std::ranges::filter_view::base

| | (1) | (since C++20) | | | ---------------------- | ------------- | ------------- | | constexpr V base() &&; | (2) | (since C++20) |

1. Equivalent to return base_;.

2. Equivalent to return std::move(base_);.

std::ranges::filter_view::pred

| constexpr const Pred& pred() const; | | (since C++20) | | ----------------------------------- | | ------------- |

Returns a reference to the contained Pred object. The behavior is undefined if _pred_ does not contain a value.

std::ranges::filter_view::begin

| constexpr /*iterator*/ begin(); | | (exposition only*) | | --------------------------------- | | ------------------- |

In order to provide the amortized constant time complexity required by the range concept, this function caches the result within the filter_view object for use on subsequent calls. Equivalent to

The behavior is undefined if _pred_ does not contain a value.

std::ranges::filter_view::end

| constexpr auto end(); | | (since C++20) | | --------------------- | | ------------- |

Returns an iterator to the end. Equivalent to

[edit] Deduction guides

| template< class R, class Pred >filter_view( R&&, Pred ) -> filter_view<views::all_t<R>, Pred>; | | (since C++20) | | ------------------------------------------------------------------------------------------------------------------------- | | ------------- |

[edit] Nested classes

| | the iterator type of filter_view(exposition-only member class*) | | --------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | the sentinel type of filter_view when the underlying view is not a common_range(exposition-only member class*) |

[edit] Example

#include #include   int main() { auto even = [](int i) { return 0 == i % 2; }; auto square = [](int i) { return i * i; };   for (int i : std::views::iota(0, 6) | std::views::filter(even) | std::views::transform(square)) std::cout << i << ' '; std::cout << '\n'; }

Output:

[edit] Defect reports

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

[edit] See also