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std::ranges::drop_view<V>::begin

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

Range primitives



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(until C++23)(C++23)


 
 
constexpr auto begin()

    requires (!(__SimpleView<V> &&
                 ranges::random_access_range<const V> &&

                 ranges::sized_range<const V>));
(1) (since C++20)
constexpr auto begin() const

    requires ranges::random_access_range<const V> &&

             ranges::sized_range<const V>;
(2) (since C++20)

Returns an iterator to the first element of the drop_view, that is, an iterator to the Nth element of the underlying view, or to the end of the underlying view if it has less than N elements.

If V is not a random_access_range or a sized_range, in order to provide the amortized constant time complexity required by the range concept, the overload (1) caches the result within the drop_view object for use on subsequent calls.

Contents

[edit] Parameters

(none)

[edit] Return value

ranges::next(ranges::begin(base_), count_, ranges::end(base_)), where base_ is the underlying view, and count_ is the number of elements to skip.

[edit] Example

#include <array>
#include <concepts>
#include <iostream>
#include <iterator>
#include <ranges>
 
void println(std::ranges::range auto const& range)
{
    for (auto const& elem : range)
        std::cout << elem;
    std::cout << '\n';
}
 
int main()
{
    std::array hi{'H', 'e', 'l', 'l', 'o', ',', ' ', 'C', '+', '+', '2', '0', '!'};
    println(hi);
 
    const auto pos = std::distance(hi.begin(), std::ranges::find(hi, 'C'));
    auto cxx = std::ranges::drop_view{hi, pos};
    std::cout << "*drop_view::begin() == '" << *cxx.begin() << "'\n";
//  *cxx.begin() = 'c'; // undefined: 'views' are to be used as observers
    println(cxx);
}

Output:

Hello, C++20!
*drop_view::begin() == 'C'
C++20!

[edit] Defect reports

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

DR Applied to Behavior as published Correct behavior
LWG 3482 C++20 the const overload can be called with unsized ranges the const overload requires sized_range

[edit] See also

(C++20)
returns an iterator or a sentinel to the end
(public member function) [edit]
returns an iterator to the beginning of a range
(customization point object)[edit]
returns a sentinel indicating the end of a range
(customization point object)[edit]