std::ranges::take_view<V>::begin

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< cpp‎ | ranges‎ | take view
 
 
Ranges library
Range access
Range conversions
(C++23)
Range primitives



Dangling iterator handling
Range concepts
Views

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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.

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).

Parameters

(none)

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

ranges::range_difference_t<Base_>(this->size()))

no std::counted_iterator(ranges::begin(base_), count_)

Example

#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';
}

Output:

∀x

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 integer-class types might fail made explicit

See also

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