std::ranges::views::take_while,std::ranges::take_while_view

From cppreference.com

Compiler support
Freestanding and hosted
Language
Standard library
Standard library headers
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

[edit]

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::take_while_view

Member functions
take_while_view::take_while_view
take_while_view::base
take_while_view::pred
take_while_view::begin
take_while_view::end
Deduction guides
Sentinel
take_while_view::sentinel::sentinel
take_while_view::sentinel::base
operator==(take_while_view::sentinel)

[edit]

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 take_while_view :publicranges::view_interface<take_while_view<V, Pred>>	(1)	(since C++20)
namespace views{ inlineconstexpr/unspecified/ take_while=/unspecified/; }	(2)	(since C++20)
Call signature
template<ranges::viewable_range R,class Pred> requires/* see below */ constexprranges::viewauto take_while( R&& r, Pred&& pred);		(since C++20)
template<class Pred> constexpr/range adaptor closure/ take_while( Pred&& pred);		(since C++20)

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

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

take_while_view models the conceptscontiguous_range,random_access_range,bidirectional_range,forward_range, andinput_range when the underlying viewV models respective concepts.

[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*)

[edit]Member functions

(constructor)	constructs a`take_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 a sentinel representing 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]
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]
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]Nested classes

sentinel

the sentinel type
(exposition-only member class template*)

[edit]Notes

Forforward_iterators,views::take_while(v, pred) is similar toranges::subrange{ranges::begin(v),ranges::find_if_not(v, pred)}, but the latter invokespred only during construction (while the former invokespred each time a validtake_while iterator is compared to a sentinel).

[edit]Example

Run this code

#include <iostream>#include <ranges> int main(){for(int year: std::views::iota(2020)| std::views::take_while([](int y){return y<2026;}))std::cout<< year<<' ';std::cout<<'\n'; constchar note[]{"Today is yesterday's tomorrow!..."};auto not_dot=[](char c){return c!='.';};for(char x: std::ranges::take_while_view(note, not_dot))std::cout<< x;std::cout<<'\n';}

Output:

2020 2021 2022 2023 2024 2025Today is yesterday's tomorrow!

[edit]See also

ranges::take_viewviews::take (C++20)	a`view` consisting of the first N elements of another`view` (class template)(range adaptor object)[edit]
ranges::drop_while_viewviews::drop_while (C++20)	a`view` consisting of the elements of another`view`, skipping the initial subsequence of elements until the first element where the predicate returnsfalse (class template)(range adaptor object)[edit]