ref_view class (C++ Standard Library)

A view that references the elements that belong to another range.

Syntax

template<std::ranges::range R>
    requires std::is_object_v<R>
class ref_view : public ranges::view_interface<ref_view<R>>;

Template parameters

R
The range to reference.

Members

Member functions	Description
ConstructorsC++20	Construct a ref_view.
baseC++20	Get a reference to the underlying range.
beginC++20	Get an iterator to the first element.
dataC++20	Get a pointer to the first element in the referenced range.
emptyC++20	Test whether this ref_view is empty.
endC++20	Get the sentinel at the end of this ref_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.
frontC++20	Get the first element.
operator[]C++20	Get the element at the specified position.
operator boolC++20	Test whether this ref_view isn't empty.

View characteristics

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

Characteristic	Description
Range adaptor	views::all or views::common
Underlying range	Must satisfy input_range
Element type	Same as the underlying range
View iterator category	Same as the underlying range
Sized	Only if the underlying range satisfies sized_range
Is const-iterable	Yes
Common range	Only if the underlying range satisfies common_range
Borrowed range	Yes

Requirements

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

Namespace: std::ranges

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

Constructors

Construct an instance of a ref_view

// construct a ref_view from a range
template<different-from<ref_view> R>
constexpr ref_view(R&& rg);

Parameters

rg
The range to reference.

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

Return value

A ref_view instance.

Remarks

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

A ref_view is useful for converting a container to a view. For example, you can use ref_view to convert a vector to a view, which makes it inexpensive to pass the elements of the vector around.

Example: ref_view

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

int main()
{
    std::vector<int> v = {1,2,3};
    auto refView = std::views::all(v);
    std::cout << &refView[1] << " : " << &v[1]; // outputs two identical memory addresses, e.g. 00000239AFAFDF90 : 00000239AFAFDF90
    refView[0] = 10; // modifies v[0]
    std::cout << "\n" << v[0]; // 10
}

00000239AFAFDF90 : 00000239AFAFDF90
10

base

Gets a copy of the underlying range.

constexpr R& base() const;

Parameters

None.

Return value

The underlying range.

begin

Get an iterator to the first element in the ref_view.

constexpr iterator_t<R> begin() const;

Parameters

None.

Return value

An iterator pointing at the first element in this ref_view.

data

Get a pointer to the first element in this ref_view. The elements in the range must be contiguous.

constexpr auto data() const requires contiguous_range<R>;

Parameters

None.

Return value

A pointer to the first element.

empty

Test whether this ref_view is empty.

constexpr bool empty() const

Parameters

None.

Return value

Returns true if the ref_view contains no elements. Otherwise, false.

end

Get the sentinel at the end of this ref_view.

constexpr sentinel_t<R> end() const

Return value

The sentinel that follows the last element in this ref_view:

size

Get the number of elements.

constexpr auto size() const requires sized_range<R>

Parameters

None.

Return value

The number of elements in the ref_view.

See also

<ranges>
all range adaptor
view classes