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std::ranges::take_view::begin(3) C++ Standard Libary std::ranges::take_view::begin(3)


std::ranges::take_view::begin - std::ranges::take_view::begin


constexpr auto begin() requires (!__SimpleView<V>); (1) (since C++20)
constexpr auto begin() const requires ranges::range<const V>; (2) (since C++20)

Returns an iterator to the first element of the take_view.

1) Returns a std::counted_iterator or a ranges::iterator_t<V>.
2) Returns a std::counted_iterator or a ranges::iterator_t<const V>.

Overload (1) does not participate in overload resolution if V is a simple view (that
is, if V and const V are views with the same iterator and sentinel types).



Return value

The result depends on the concepts satisfied by possible const-qualified underlying
view type Base_, which is V (for overload (1)) or const V (for overload (2)).

Let base_ be the underlying view, count_ be the number passed to the constructor
(0 if default initialized).

The underlying random_access_range
view satisfies
... yes no
sized_range yes ranges::begin(base_)
no std::counted_iterator(ranges::begin(base_), count_)


// Run this code

#include <ranges>
#include <iostream>
#include <string_view>
using namespace std::literals;

int main()
static constexpr auto sv = {"∀x"sv, "∃y"sv, "ε"sv, "δ"sv};

std::cout << *std::ranges::take_view(sv, 8).begin() << '\n';



Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
P2393R1 C++20 implicit conversions between signed and unsigned made explicit
integer-class types might fail

See also

end returns an iterator or a sentinel to the end
(C++20) (public member function)
counted_iterator iterator adaptor that tracks the distance to the end of the range
(C++20) (class template)
operator== compares a sentinel with an iterator returned from take_view::begin
(C++20) (function)