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

 

C++

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Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Ranges library

Range access
begin cbegin end cend	rbegin crbegin rend crend	size ssize data cdata	empty
Range conversions
to (C++23)
Range primitives
range_size_trange_difference_t range_value_t	range_reference_trange_const_reference_trange_rvalue_reference_t   (C++23)	iterator_tconst_iterator_tsentinel_t (C++23)
Dangling iterator handling
dangling	borrowed_iterator_t	borrowed_subrange_t
Range concepts
range borrowed_range    sized_range constant_range (C++23)	common_range view viewable_range	input_range output_range forward_range	bidirectional_range random_access_range contiguous_range
Views
view_interface	subrange
Factories
empty_viewviews::empty iota_viewviews::iota	single_viewviews::single basic_istream_viewviews::istream	repeat_viewviews::repeat (C++23)(C++23)
Adaptors
ref_view views::all_tviews::all common_viewviews::common owning_view views::counted reverse_viewviews::reverse zip_viewviews::zip (C++23)(C++23) as_const_viewviews::as_const (C++23)(C++23) as_rvalue_viewviews::as_rvalue (C++23)(C++23)	take_viewviews::take take_while_viewviews::take_while drop_viewviews::drop drop_while_viewviews::drop_while zip_transform_viewviews::zip_transform (C++23)(C++23) adjacent_transform_viewviews::adjacent_transform (C++23)(C++23)   cartesian_product_viewviews::cartesian_product (C++23)(C++23)	elements_viewviews::elements keys_viewviews::keys values_viewviews::values transform_viewviews::transform adjacent_viewviews::adjacent (C++23)(C++23) slide_viewviews::slide (C++23)(C++23) stride_viewviews::stride (C++23)(C++23)	filter_viewviews::filter join_viewviews::join split_viewviews::split lazy_split_viewviews::lazy_split join_with_viewviews::join_with (C++23)(C++23) chunk_viewviews::chunk (C++23)(C++23) chunk_by_viewviews::chunk_by (C++23)(C++23)
Range adaptor objects
Range adaptor closure objects
Helper items
copyable-box	simple-view

 

std::ranges::take_while_view

Member functions

take_while_view::take_while_view (C++20)

take_while_view::base (C++20)

take_while_view::pred (C++20)

take_while_view::begin (C++20)

take_while_view::end (C++20)

Deduction guides

Sentinel

take_while_view::sentinel::sentinel (C++20)

take_while_view::sentinel::base (C++20)

operator==(take_while_view::sentinel) (C++20)

 

Defined in header <ranges>
template< ranges::view V, class Pred >     requires ranges::input_range<V> &&              std::is_object_v<Pred> &&              std::indirect_unary_predicate<const Pred, ranges::iterator_t<V>> class take_while_view : public ranges::view_interface<take_while_view<V, Pred>>	(1)	(since C++20)
namespace views {     inline constexpr /*unspecified*/ take_while = /*unspecified*/; }	(2)	(since C++20)
Call signature
template< ranges::viewable_range R, class Pred >     requires /* see below */ constexpr ranges::view auto 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 represents view of the elements from an underlying sequence, starting at the beginning and ending at the first element for which the predicate returns false.

2) Range adaptor object. The expression views::take_while(e, f) is expression-equivalent to take_while_view(e, f) for any suitable subexpressions e and f.

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

Expression-equivalent

Expression e is expression-equivalent to expression f, if

• e and f have the same effects, and
• either both are constant subexpressions or else neither is a constant subexpression, and
• either both are potentially-throwing or else neither is potentially-throwing (i.e. noexcept(e) == noexcept(f)).

Member functions

(constructor) (C++20)	constructs a take_while_view (public member function)
base (C++20)	returns a copy of the underlying (adapted) view (public member function)
pred (C++20)	returns a reference to the stored predicate (public member function)
begin (C++20)	returns an iterator to the beginning (public member function)
end (C++20)	returns a sentinel representing the end (public member function)
Inherited from std::ranges::view_interface
empty (C++20)	Returns whether the derived view is empty. Provided if it satisfies sized_range or forward_range. (public member function of std::ranges::view_interface<D>)
operator bool (C++20)	Returns whether the derived view is not empty. Provided if ranges::empty is applicable to it. (public member function of std::ranges::view_interface<D>)
data (C++20)	Gets the address of derived view's data. Provided if its iterator type satisfies contiguous_iterator. (public member function of std::ranges::view_interface<D>)
front (C++20)	Returns the first element in the derived view. Provided if it satisfies forward_range. (public member function of std::ranges::view_interface<D>)
operator[] (C++20)	Returns the nth element in the derived view. Provided if it satisfies random_access_range. (public member function of std::ranges::view_interface<D>)

Nested classes

sentinel

the sentinel type (exposition-only member class template)

Example

Run this code

#include <ranges>
#include <iostream>
 
int main()
{
    for (int year : std::views::iota(2017)
                  | std::views::take_while([](int y) { return y <= 2020; })) {
        std::cout << year << ' ';
    }
    std::cout << '\n';
 
    const char idea[] {"Today is yesterday's tomorrow!.."};
    for (char x : std::ranges::take_while_view(idea, [](char c) { return c != '.'; })) {
        std::cout << x;
    }
    std::cout << '\n';
}

Output:

2017 2018 2019 2020 
Today is yesterday's tomorrow!

See also

ranges::take_viewviews::take (C++20)	a view consisting of the first N elements of another view (class template) (range adaptor object)
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 returns false (class template) (range adaptor object)