std::ranges::views::drop, std::ranges::drop_view

template< ranges::view V >
class drop_view
    : public ranges::view_interface<drop_view<V>>

namespace views {
    inline constexpr /* unspecified */ drop = /* unspecified */;
}

template< ranges::viewable_range R >
    requires /* see below */
constexpr ranges::view auto
    drop( R&& r, ranges::range_difference_t<R> count );

template< class DifferenceType >
constexpr /* range adaptor closure */ drop( DifferenceType&& count );

• ((void)f, decay-copy(e)), if T is a ranges::empty_view, except that the evaluations of e and f are indeterminately sequenced;
• otherwise, T(ranges::begin(e) + inc, ranges::end(e),/*to-unsigned-like*/(ranges::distance(e) - inc)), if T is a specialization of ranges::subrange that models both random_access_range and sized_range, and T needs to store the size (see ranges::subrange::subrange() for details), where inc is std::min<D>(ranges::distance(e), f);
• otherwise, U(ranges::begin(e) + inc, ranges::end(e)), if T is a specialization of std::span, std::basic_string_view, ranges::iota_view, or ranges::subrange that models both random_access_range and sized_range, where U is
• std::span<typenameT::element_type>, if T is a specialization of std::span;
• T otherwise;

• otherwise, drop_view(e, f).

drop_view models the concepts contiguous_range, random_access_range, bidirectional_range, forward_range, input_range, common_range, and sized_range when the underlying view V models respective concepts.

Data members

Member functions

Deduction guides

Helper templates

template< class T >
constexpr bool enable_borrowed_range<std::ranges::drop_view<T>> =
    ranges::enable_borrowed_range<T>;

This specialization of ranges::enable_borrowed_range makes drop_view satisfy borrowed_range when the underlying view satisfies it.

Example

#include <initializer_list>
#include <iostream>
#include <ranges>

int main()
{
    const auto nums = {1, 2, 3, 4, 5, 6, 7};

    std::cout << "drop " << 2 << ": ";
    for (int i : std::ranges::drop_view{nums, 2})
        std::cout << i << ' ';
    std::cout << '\n';

    std::cout << "drop " << 3 << ": ";
    for (int i : nums | std::views::drop(3))
        std::cout << i << ' ';
    std::cout << '\n';

    std::cout << "drop " << 4 << ": ";
    for (int i : std::views::iota(1, 8) | std::views::drop(4))
        std::cout << i << ' ';
    std::cout << '\n';

    // Note that dropping more than the number of elements is OK:
    for (int dp : {5, 6, 7, 890, 100500})
    {
        std::cout << "drop " << dp << ": ";
        for (int i : std::views::iota(1, 8) | std::views::drop(dp))
            std::cout << i << ' ';
        std::cout << '\n';
    }
}

drop 2: 3 4 5 6 7
drop 3: 4 5 6 7
drop 4: 5 6 7
drop 5: 6 7
drop 6: 7
drop 7:
drop 890: 
drop 100500:

Defect reports

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

See also