std::ranges::concat_view<Views...>::size

 

C++

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Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Diagnostics library

Memory management library

Metaprogramming library (C++11)

General utilities library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library (C++17)

Concurrency support library (C++11)

Execution control library (C++26)

Technical specifications

Symbols index

External libraries

 

Ranges library

Range access begin cbegin   end cend rbegin crbegin   rend crend size ssize   data cdata reserve_hint (C++26)   empty

Range conversions std::from_range_t std::from_range (C++23)(C++23)     to (C++23)

Dangling iterator handling dangling borrowed_iterator_t borrowed_subrange_t

Range primitives
range_size_trange_difference_trange_value_t elements_of (C++23)	iterator_tconst_iterator_tsentinel_tconst_sentinel_t (C++23)(C++23)	range_reference_trange_const_reference_trange_rvalue_reference_trange_common_reference_t (C++23)

Range concepts
range borrowed_range    common_range	sized_range viewable_range    view	input_range output_range forward_range	bidirectional_range    random_access_range contiguous_range	approximately_sized_range (C++26) constant_range (C++23)

Views
view_interface	subrange

Range factories
empty_viewviews::empty	single_viewviews::single	basic_istream_viewviews::istream	iota_viewviews::iota	repeat_viewviews::repeat (C++23)(C++23)

Range adaptors
views::all_tviews::all as_rvalue_viewviews::as_rvalue (C++23)(C++23)   filter_viewviews::filter transform_viewviews::transform take_viewviews::take take_while_viewviews::take_while common_viewviews::common views::counted as_input_viewviews::as_input (C++26)(C++26)	ref_view drop_viewviews::drop drop_while_viewviews::drop_while lazy_split_viewviews::lazy_split split_viewviews::split join_viewviews::join join_with_viewviews::join_with (C++23)(C++23)   concat_viewviews::concat (C++26)(C++26) cache_latest_viewviews::cache_latest (C++26)(C++26)	owning_view reverse_viewviews::reverse as_const_viewviews::as_const (C++23)(C++23) elements_viewviews::elements keys_viewviews::keys values_viewviews::values enumerate_viewviews::enumerate (C++23)(C++23) zip_viewviews::zip (C++23)(C++23) zip_transform_viewviews::zip_transform (C++23)(C++23)	adjacent_viewviews::adjacent (C++23)(C++23) views::pairwise (C++23) adjacent_transform_viewviews::adjacent_transform (C++23)(C++23) views::pairwise_transform (C++23) chunk_viewviews::chunk (C++23)(C++23) slide_viewviews::slide (C++23)(C++23) chunk_by_viewviews::chunk_by (C++23)(C++23) stride_viewviews::stride (C++23)(C++23) cartesian_product_viewviews::cartesian_product (C++23)(C++23)

Range generators std::generator (C++23)

Range adaptor closure objects range_adaptor_closure (C++23)

Range adaptor objects

Helper items
copyable-box movable-box (until C++23)  (C++23)	simple-view non-propagating-cache

 

std::ranges::concat_view

Member functions

concat_view::concat_view

concat_view::begin

concat_view::end

concat_view::size

Deduction guides

Iterator

Member functions

concat_view::iterator::iterator

concat_view::iterator::operator*

concat_view::iterator::operator[]

concat_view::iterator::operator++ concat_view::iterator::operator++(int) concat_view::iterator::operator-- concat_view::iterator::operator--(int) concat_view::iterator::operator+= concat_view::iterator::operator-=

concat_view::iterator::satisfy concat_view::iterator::prev concat_view::iterator::advance-fwd concat_view::iterator::advance-bwd

Non-member functions

operator==(concat_view::iterator) operator<(concat_view::iterator) operator>(concat_view::iterator) operator<=(concat_view::iterator) operator>=(concat_view::iterator) operator<=>(concat_view::iterator)

operator+(concat_view::iterator) operator-(concat_view::iterator)

iter_move(concat_view::iterator)

iter_swap(concat_view::iterator)

 

constexpr auto size() requires(sized_range<Views> && ...);	(1)	(since C++26)
constexpr auto size() const requires(sized_range<const Views> && ...);	(2)	(since C++26)

Returns the number of elements.

Equivalent to return std::apply
       (
           [](auto... sizes)
           {
               using CT = ranges::common_type_t<decltype(sizes)...>;
               return (make-unsigned-like-t <CT>(sizes) + ...);
           },
           tuple-transform (ranges::size, views_ )
       ); .

Return value

As described above.

Complexity

Constant.

Notes

The complexity of concat_view is constant time (even though in some cases it is a linear function of the number of ranges it concatenates which is a statically known parameter of this view) because time complexity as required by the ranges concepts are formally expressed with respect to the total number of elements (the size) of a given range, and not to the statically known parameters of that range.

Example

The preliminary version can be checked out on Compiler Explorer.

Run this code

#include <cassert>
#include <forward_list>
#include <list>
#include <ranges>

int main()
{
    constexpr static auto a = {1, 2};
    constexpr static auto b = {1, 2, 3};
    constexpr static auto c = {1, 2, 3, 4};
    
    constexpr auto con{std::views::concat(a, b, c)};
    static_assert(std::ranges::sized_range<decltype(con)>);
    static_assert(con.size() == 2 + 3 + 4);
    
    std::forward_list d = b;
    static_assert(not std::ranges::sized_range<std::forward_list<int>>);
    const auto cat{std::views::concat(b, c, d)};
    static_assert(not std::ranges::sized_range<decltype(cat)>);
//  auto x = cat.size(); // error: cat is not sized_range because of d
    
    std::list e = c;
    const auto dog{std::views::concat(a, b, e)};
    static_assert(std::ranges::sized_range<decltype(dog)>);
    assert(dog.size() == 2 + 3 + 4);
}

See also

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