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

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

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)

Atomic operations library (C++11)

Thread support library (C++11)

Technical Specifications

 

Ranges library

Range access
begin cbegin end cend	rbegin crbegin rend crend	size ssize data cdata	empty
Range primitives
iterator_tsentinel_t	range_size_trange_difference_t	range_value_t	range_reference_trange_rvalue_reference_t
Dangling iterator handling
dangling	borrowed_iterator_t	borrowed_subrange_t
Range concepts
range borrowed_range sized_range	common_range view viewable_range	input_range output_range forward_range	bidirectional_range random_access_range contiguous_range
Views
view_interface	subrange
Semiregular wrapper
Factories
empty_viewviews::empty	single_viewviews::single	iota_viewviews::iota	views::counted
Adaptors
views::all_tviews::all join_viewviews::join take_viewviews::take basic_istream_viewistream_view	ref_view                                split_viewviews::split take_while_viewviews::take_while elements_viewviews::elements	common_viewviews::common transform_viewviews::transform drop_viewviews::drop keys_viewviews::keys	reverse_viewviews::reverse filter_viewviews::filter drop_while_viewviews::drop_while values_viewviews::values

 

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

 

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 drop_while_view : public ranges::view_interface<drop_while_view<V, Pred>>	(1)	(since C++20)
namespace views {     inline constexpr /*unspecified*/ drop_while = /*unspecified*/; }	(2)	(since C++20)

1) A range adaptor that represents view of elements from an underlying sequence, beginning at the first element for which the predicate returns false.

2) The expression views::drop_while(E, F) is expression-equivalent to drop_while_view{E, F} for any suitable subexpressions E and F.

drop_while_view models the concepts contiguous_range, random_access_range, bidirectional_range, forward_range, input_range, and common_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, either are both potentially-throwing or are both not potentially-throwing (i.e. noexcept(e) == noexcept(f)), and either are both constant subexpressions or are both not constant subexpressions.

Member functions

(constructor)	constructs a drop_while_view (public member function)
base	returns a copy of the underlying (adapted) view (public member function)
pred	returns a reference to the stored predicate (public member function)
begin	returns an iterator to the beginning (public member function)
end	returns an iterator or a sentinel to the end (public member function)

Example

Run this code

#include <cctype>
#include <iomanip>
#include <iostream>
#include <ranges>
#include <string>
#include <string_view>
 
std::string trim(std::string_view const in)
{
    auto view
        = in
        | std::views::drop_while(isspace)
        | std::views::reverse
        | std::views::drop_while(isspace)
        | std::views::reverse
        ;
    return {view.begin(), view.end()};
}
 
int main()
{
    const auto s = trim(" \f\n\t\r\vHello, C++20!\f\n\t\r\v ");
    std::cout << std::quoted(s) << '\n';
 
    static constexpr auto v = {0, 1, 2, 3, 4, 5};
    for (int n : v | std::views::drop_while([](int i) { return i < 3; })) {
        std::cout << n << ' ';
    }
}

Output:

"Hello, C++20!"
3 4 5