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std::ranges::views::take_while, std::ranges::take_while_view - cppreference.com

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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.

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.

Data members

Member Description
V base_ (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*)

Member functions

constructs a take_while_view
(public member function) [edit]
returns a copy of the underlying (adapted) view
(public member function) [edit]
returns a reference to the stored predicate
(public member function) [edit]
returns an iterator to the beginning
(public member function) [edit]
returns a sentinel representing the end
(public member function) [edit]
Inherited from ranges::view_interface
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]

(C++23)

 returns a constant iterator to the beginning of the range
(public member function of std::ranges::view_interface<D>) [edit]

(C++23)

 returns a sentinel for the constant iterator of the range
(public member function of std::ranges::view_interface<D>) [edit]
returns whether the derived view is not empty, provided only if ranges::empty is applicable to it
(public member function of std::ranges::view_interface<D>) [edit]
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]
returns the first element in the derived view, provided if it satisfies forward_range
(public member function of std::ranges::view_interface<D>) [edit]
returns the nth element in the derived view, provided only if it satisfies random_access_range
(public member function of std::ranges::view_interface<D>) [edit]

Deduction guides

Nested classes

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

Notes

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

Example

#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';

    const char 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 2025
Today is yesterday's tomorrow!

See also