take_view class (C++ Standard Library)

A view of the first N elements from another view.

Syntax

template<view V>
class take_view : public view_interface<take_view<V>>;

Template parameters

V
The type of the underlying range.

View characteristics

For a description of the following entries, see View class characteristics

Characteristic	Description
Range adaptor	views::take
Underlying range	Any range
Element type	Same as the underlying range
View iterator category	Same as the underlying range
Sized	No
Is const-iterable	Only if the underlying range is const iterable
Common range	Only if the underlying range satisfies random_access_range and sized_range
Borrowed range	Only if the underlying range is borrowed_range

Members

Member functions	Description
Constructors	Construct the view.
baseC++20	Get the underlying range.
beginC++20	Get an iterator to the first element.
endC++20	Get the sentinel at the end of the view.
sizeC++20	Get the number of elements. The underlying range must satisfy sized_range.
Inherited from view_interface	Description
backC++20	Get the last element.
dataC++20	Get a pointer to the first element.
emptyC++20	Test whether the view is empty.
frontC++20	Get the first element.
operator[]C++20	Get the element at the specified position.
operator boolC++20	Test whether the view isn't empty.

Requirements

Header: <ranges> (since C++20)

Namespace: std::ranges

Compiler Option: /std:c++20 or later is required.

Constructors

Construct an instance of a take_view

1) take_view() requires default_initializable<V> = default;
2) constexpr take_view(V base, range_difference_t<V> count);

Parameters

base
The underlying view.

count
The number of elements to take from the front of the underlying view. If count is more than the number of elements in the underlying view, the view will contain all the elements in the underlying range.

For information about the template parameter type, see Template parameters.

Return value

A take_view, which is a view of the first N elements from another view. If you specify more elements to drop than exist in the underlying range, an empty_view is returned.

Remarks

The best way to create a take_view is by using the views::take range adaptor. Range adaptors are the intended way to create view classes. The view types are only exposed in case you want to create your own custom view type.

1) Create a take_view that has no elements. The underlying view is default constructed. base() returns a copy of V().
2) Create a take_view from a base and a count. base is moved via std::move().

If count is less than the number of elements in the underlying range, then count determines the size of the take_view.
If count is greater than the number of elements in the underlying range, then the take_view includes all of the elements in the underlying range.

Example: take_view

// requires /std:c++20 or later
#include <ranges>
#include <iostream>
#include <vector>

int main()
{
    std::vector<int> v{0, 1, 2, 3, 4, 5, 6};
   
    auto newView = std::views::take(v, 3);
    
    for (auto& e : newView)
    {
        std::cout << e << ' '; // 0 1 2
    }
    std::cout << '\n';

    // Use the '|' operator to create a take_view
    for (auto i : v | std::views::take(3))
    {
        std::cout << i << ' '; // 0 1 2
    }
}

0 1 2
0 1 2

base

Gets a copy of the underlying view.

// Uses a copy constructor to return the underlying view
1) constexpr V base() const & requires std::copy_constructible<V>;

// Uses a move constructor to return the underlying view
2) constexpr V base() &&;

Parameters

None.

Return value

The underlying view.

begin

Get an iterator to the first element in the view.

constexpr auto begin() requires (!Simple_view<V>);
constexpr auto begin() const requires range<const V>;

Parameters

None.

Return value

An iterator pointing at the first element in the view.

Remarks

For 1, the Simple_view<V> requirement means that the view V and const V must have the same iterator and sentinel types.

end

Get the sentinel at the end of the view.

1) constexpr auto end() requires !(Simple_view<V>);
2) constexpr auto end() const requires range<const V>;

Parameters

None.

Return value

The sentinel that follows the last element in the view.

Remarks

For 1, the Simple_view<V> requirement means that the view V and const V must have the same iterator and sentinel types.

size

Get the number of elements.

constexpr auto size() requires sized_range<V>;
constexpr auto size() const requires sized_range<const V>;

Parameters

None.

Return value

The number of elements in the take_view.
If the take_view was constructed with an explicit count:

• if count is less than the number of elements in the underlying range, it's returned as the size of the view.
• if count is greater than the number of elements in the underlying range, then the size of the view is ranges::size(base).

See also

<ranges>
take range adaptor
view classes