W3cubDocs

/C++

std::ranges::slide_view<V>::size

constexpr auto size()
  requires ranges::sized_range<V>;
(since C++23)
constexpr auto size() const
  requires ranges::sized_range<const V>;
(since C++23)

Returns the number of elements.

Let base_ and n_ be the underlying view and "window size" respectively.

Equivalent to:

auto sz = ranges::distance(base_) - n_ + 1;
if (sz < 0)
    sz = 0;
return __to_unsigned_like(sz);

Parameters

(none).

Return value

The number of elements. Equals to ​0​, if the number of elements (ranges::size(base_)) in underlying view base_ is less than "window size" n_.

Example

A link to test: Compiler Explorer.

#include <forward_list>
#include <iostream>
#include <list>
#include <ranges>
 
int main()
{
    constexpr static auto v = {1, 2, 3, 4, 5, 6};
 
    constexpr int width1{4};
    constexpr auto view1{std::views::slide(v, width1)};
    static_assert(view1.size() == 3);
    static_assert(view1.size() == (v.size() - width1 + 1));
 
    constexpr int width2{8};
    constexpr auto view2{std::views::slide(v, width2)};
    // window is too wide, so view2 has no elements:
    static_assert(view2.size() == 0);
 
    std::forward_list forward_list = v;
    const auto view3{std::views::slide(forward_list, width1)};
//  auto x = view3.size(); // error: sized_range constraint is not satisfied
 
    std::list list = v;
    const auto view4{std::views::slide(list, width1)};
    std::cout << view4.size() << '\n'; // prints 3
}

Output:

3

See also

(C++20)
returns an integer equal to the size of a range
(customization point object)
(C++20)
returns a signed integer equal to the size of a range
(customization point object)

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/ranges/slide_view/size