From cppreference.com
Defined in header
template<ranges::viewV>classdrop_view:publicranges::view_interface<drop_view<V>> (1) (since C++20)namespaceviews{inlineconstexpr/* unspecified */drop=/* unspecified */;} (2) (since C++20)Call signature
template<ranges::viewable_rangeR>requires/* see below */constexprranges::viewautodrop(R&&r,ranges::range_difference_t<R>count);(since C++20)template<classDifferenceType>constexpr/* range adaptor closure */drop(DifferenceType&&count);(since C++20)1) A range adaptor consisting of elements of the underlying sequence, skipping the first N elements.
2)
. Given T is std::remove_cvref_t<decltype((e))> and D is ranges::range_difference_t<decltype((e))>), the expression views::drop(e,f) is
to:
((void)f,
(e)), if T is a
, 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
and
, and T needs to store the size (see
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,
, ranges::iota_view, or ranges::subrange that models both
and
, where U is
std::span<typenameT::element_type>, if T is a specialization of std::span;
T otherwise;
otherwise, if T is a specialization of
:
views::repeat(*e.value_,ranges::distance(e)-inc), if T models
; in such case e is evaluated only once;
((void)e,auto(f)) otherwise, except that the evaluations of e and f are indeterminately sequenced;
(since C++23)otherwise, drop_view(e,f).
In all cases, decltype((f)) must model std::convertible_to<D>.
drop_view models the concepts
,
,
,
,
,
, and
when the underlying view V models respective concepts.
Data members
Member Description Vbase_(private)the underlying view
(exposition-only member object*)ranges::range_difference_t<V>count_(private)the number of elements to skip
(exposition-only member object*)
<ranges::iterator_t<V>>cache_(private)
(present only if V satisfies
but not
and
)an object that caches the result of calls to
(exposition-only member object*)Member functions
constructs a drop_view
(public member function)
returns a copy of the underlying (adapted) view
(public member function)
returns an iterator to the beginning
(public member function)
returns an iterator or a sentinel to the end
(public member function)
returns the number of elements, provided only if the underlying (adapted) range satisfies
(public member function)
(C++26)
returns the approximate size of the resulting
(public member function)
Inherited from
returns whether the derived view is empty, provided only if it satisfies
or
(public member function of std::ranges::view_interface<D>)
(C++23)
returns a constant iterator to the beginning of the range
(public member function of std::ranges::view_interface<D>)
(C++23)
returns a sentinel for the constant iterator of the range
(public member function of std::ranges::view_interface<D>)
returns whether the derived view is not empty, provided only if
is applicable to it
(public member function of std::ranges::view_interface<D>)
gets the address of derived view's data, provided only if its iterator type satisfies
(public member function of std::ranges::view_interface<D>)
returns the first element in the derived view, provided if it satisfies
(public member function of std::ranges::view_interface<D>)
returns the last element in the derived view, provided only if it satisfies
and
(public member function of std::ranges::view_interface<D>)
returns the nth element in the derived view, provided only if it satisfies
(public member function of std::ranges::view_interface<D>)
Helper templates
template<classT>constexprboolenable_borrowed_range<std::ranges::drop_view<T>>=ranges::enable_borrowed_range<T>;(since C++20)This specialization of
makes drop_view satisfy
when the underlying view satisfies it.
Example
Run this code
#include<initializer_list>#include<iostream>#include<ranges>intmain(){constautonums={1,2,3,4,5,6,7};std::cout<<"drop "<<2<<": ";for(inti:std::ranges::drop_view{nums,2})std::cout<<i<<' ';std::cout<<'\n';std::cout<<"drop "<<3<<": ";for(inti:nums|std::views::drop(3))std::cout<<i<<' ';std::cout<<'\n';std::cout<<"drop "<<4<<": ";for(inti: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(intdp:{5,6,7,890,100500}){std::cout<<"drop "<<dp<<": ";for(inti:std::views::iota(1,8)|std::views::drop(dp))std::cout<<i<<' ';std::cout<<'\n';}}Output:
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.
DR Applied to Behavior as published Correct behavior
C++20 views::drop sometimes fails to
construct a sized random access range the construction is adjusted
so that it is always valid
C++20 drop_view was never a borrowed_rangeit is a borrowed_range if its underlying view is See also