std::ranges::views::drop_while,std::ranges::drop_while_view

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Ranges library(C++20)
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Date and time library
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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)

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
to_input_viewviews::to_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

[edit]

std::ranges::drop_while_view

Member functions
drop_while_view::drop_while_view
drop_while_view::base
drop_while_view::pred
drop_while_view::begin
drop_while_view::end
Deduction guides

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Defined in header`<ranges>`
template<ranges::view V,class Pred> requiresranges::input_range<V>&& std::is_object_v<Pred>&& std::indirect_unary_predicate<const Pred,ranges::iterator_t<V>> class drop_while_view :publicranges::view_interface<drop_while_view<V, Pred>>	(1)	(since C++20)
namespace views{ inlineconstexpr/* unspecified / drop_while=/ unspecified */; }	(2)	(since C++20)
Call signature
template<ranges::viewable_range R,class Pred> requires/* see below */ constexprranges::viewauto drop_while( R&& r, Pred&& pred);		(since C++20)
template<class Pred> constexpr/range adaptor closure/ drop_while( Pred&& pred);		(since C++20)

1) A range adaptor that representsview of elements from an underlying sequence, beginning at the first element for which the predicate returnsfalse.

2)RangeAdaptorObject. The expressionviews::drop_while(e, f) isexpression-equivalent todrop_while_view(e, f) for any suitable subexpressionse andf.

drop_while_view models the conceptscontiguous_range,random_access_range,bidirectional_range,forward_range,input_range, andcommon_range when the underlying viewV models respective concepts. It also modelssized_range ifranges::forward_range<V> andstd::sized_sentinel_for<ranges::sentinel_t<V>,ranges::iterator_t<V>> are modeled.

[edit]Data members

Member	Description
`Vbase_`(private)	the underlying view (exposition-only member object*)
`copyable-box<Pred>`(until C++23)`movable-box<Pred>`(since C++23)`pred_`(private)	the underlying function object (exposition-only member object*)
`non-propagating-cache`<ranges::iterator_t<V>>`cache_`(private) (present only if`V` satisfies`forward_range`)	an object that caches the result of`begin()` (exposition-only member object*)

[edit]Member functions

(constructor)	constructs a`drop_while_view` (public member function)[edit]
base	returns a copy of the underlying (adapted) view (public member function)[edit]
pred	returns a reference to the stored predicate (public member function)[edit]
begin	returns an iterator to the beginning (public member function)[edit]
end	returns an iterator or a sentinel to the end (public member function)[edit]
Inherited fromstd::ranges::view_interface
empty	returns whether the derived view is empty, provided only if it satisfies`sized_range` or`forward_range` (public member function of`std::ranges::view_interface<D>`)[edit]
cbegin (C++23)	returns a constant iterator to the beginning of the range (public member function of`std::ranges::view_interface<D>`)[edit]
cend (C++23)	returns a sentinel for the constant iterator of the range (public member function of`std::ranges::view_interface<D>`)[edit]
operator bool	returns whether the derived view is not empty, provided only ifranges::empty is applicable to it (public member function of`std::ranges::view_interface<D>`)[edit]
data	gets the address of derived view's data, provided only if its iterator type satisfies`contiguous_iterator` (public member function of`std::ranges::view_interface<D>`)[edit]
size	returns the number of elements in the derived view. Provided if it satisfies`forward_range` and its sentinel and iterator type satisfy`sized_sentinel_for`. (public member function of`std::ranges::view_interface<D>`)[edit]
front	returns the first element in the derived view, provided if it satisfies`forward_range` (public member function of`std::ranges::view_interface<D>`)[edit]
back	returns the last element in the derived view, provided only if it satisfies`bidirectional_range` and`common_range` (public member function of`std::ranges::view_interface<D>`)[edit]
operator[]	returns the`n`^th element in the derived view, provided only if it satisfies`random_access_range` (public member function of`std::ranges::view_interface<D>`)[edit]

[edit]Deduction guides

[edit]Helper templates

template<class T,class Pred> constexprbool enable_borrowed_range<std::ranges::drop_while_view<T, Pred>>= ranges::enable_borrowed_range<T>;		(since C++20)

This specialization ofstd::ranges::enable_borrowed_range makesdrop_while_view satisfyborrowed_range when the underlying view satisfies it.

[edit]Notes

In order to provide the amortized constant time complexity required by therange concept, the result ofbegin is cached within thedrop_while_view object. If the underlying range is modified after the first call tobegin(), subsequent uses of thedrop_while_view object might have unintuitive behavior.

[edit]Example

Run this code

#include <iostream>#include <ranges>#include <string>#include <string_view> using std::operator""sv; [[nodiscard]]constexprbool is_space(char p)noexcept{auto ne=[p](auto q){return p!= q;};return!!("\t\n\v\r\f"| std::views::drop_while(ne));}; [[nodiscard("trims the output")]]constexprstd::string_view trim_left(std::string_viewconst in)noexcept{auto view= in| std::views::drop_while(is_space);return{view.begin(), view.end()};} [[nodiscard("trims the output")]]constexprstd::string trim(std::string_viewconst in){auto view= in| std::views::drop_while(is_space)| std::views::reverse| std::views::drop_while(is_space)| std::views::reverse;return{view.begin(), view.end()};} int main(){    static_assert(trim_left("\n C++23")=="C++23"sv); constexprauto src{"\f\n\t\r\vHello, C++20!\f\n\t\r\v "sv};    static_assert(trim(src)=="Hello, C++20!"); staticconstexprauto v={0,1,2,3,4,5};for(int n: v| std::views::drop_while([](int i){return i<3;}))std::cout<< n<<' ';std::cout<<'\n';}