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

 

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技術規範

符號索引

外部庫

 

範圍庫 (Ranges library)

範圍訪問 begin cbegin   end cend rbegin crbegin   rend crend size ssize   data cdata reserve_hint (C++26)   empty

範圍轉換 (Range conversions) std::from_range_t std::from_range (C++23)(C++23)     to (C++23)

懸空迭代器處理 (Dangling iterator handling) dangling borrowed_iterator_t borrowed_subrange_t

範圍原語 (Range primitives)
range_size_trange_difference_trange_value_t elements_of (C++23)	iterator_tconst_iterator_tsentinel_tconst_sentinel_t (C++23)(C++23)	range_reference_trange_const_reference_trange_rvalue_reference_trange_common_reference_t (C++23)

範圍概念 (Range concepts)
range borrowed_range    common_range	sized_range viewable_range    view	input_range output_range forward_range	bidirectional_range    random_access_range contiguous_range	approximately_sized_range (C++26) constant_range (C++23)

檢視
view_interface	subrange

範圍工廠 (Range factories)
empty_viewviews::empty	single_viewviews::single	basic_istream_viewviews::istream	iota_viewviews::iota	repeat_viewviews::repeat (C++23)(C++23)

範圍介面卡 (Range adaptors)
views::all_tviews::all as_rvalue_viewviews::as_rvalue (C++23)(C++23)   filter_viewviews::filter transform_viewviews::transform take_viewviews::take take_while_viewviews::take_while common_viewviews::common views::counted to_input_viewviews::to_input (C++26)(C++26)	ref_view drop_viewviews::drop drop_while_viewviews::drop_while lazy_split_viewviews::lazy_split split_viewviews::split join_viewviews::join join_with_viewviews::join_with (C++23)(C++23)   concat_viewviews::concat (C++26)(C++26) cache_latest_viewviews::cache_latest (C++26)(C++26)	owning_view reverse_viewviews::reverse as_const_viewviews::as_const (C++23)(C++23) elements_viewviews::elements keys_viewviews::keys values_viewviews::values enumerate_viewviews::enumerate (C++23)(C++23) zip_viewviews::zip (C++23)(C++23) zip_transform_viewviews::zip_transform (C++23)(C++23)	adjacent_viewviews::adjacent (C++23)(C++23) views::pairwise (C++23) adjacent_transform_viewviews::adjacent_transform (C++23)(C++23) views::pairwise_transform (C++23) chunk_viewviews::chunk (C++23)(C++23) slide_viewviews::slide (C++23)(C++23) chunk_by_viewviews::chunk_by (C++23)(C++23) stride_viewviews::stride (C++23)(C++23) cartesian_product_viewviews::cartesian_product (C++23)(C++23)

範圍生成器 (Range generators) std::generator (C++23)

範圍介面卡閉包物件 (Range adaptor closure objects) range_adaptor_closure (C++23)

範圍介面卡物件 (Range adaptor objects)

輔助項 (Helper items)
copyable-box movable-box (直到 C++23)  (C++23)	simple-view non-propagating-cache

 

std::ranges::drop_view

成員函式

drop_view::drop_view

drop_view::base

drop_view::begin

drop_view::end

drop_view::size

推導指引

 

constexpr auto begin()     requires (!(/*simple-view*/<V> &&                  ranges::random_access_range<const V> &&                  ranges::sized_range<const V>));	(1)	(C++20 起)
constexpr auto begin() const     requires ranges::random_access_range<const V> &&              ranges::sized_range<const V>;	(2)	(C++20 起)

返回指向 drop_view 首元素的迭代器，即指向底層檢視的第 N 個元素的迭代器，如果底層檢視的元素少於 N 個，則返回指向底層檢視末尾的迭代器。

如果 V 不是 random_access_range 或 sized_range，為了提供 range 概念所要求的攤銷常數時間複雜度，過載 (1) 會將結果快取在底層 cache_ 物件中，以供後續呼叫使用。

返回值

ranges::next(ranges::begin(base_), count_, ranges::end(base_)).

示例

執行此程式碼

#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);
}

輸出

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

缺陷報告

下列更改行為的缺陷報告追溯地應用於以前出版的 C++ 標準。

缺陷報告	應用於	釋出時的行為	正確的行為
LWG 3482	C++20	const 過載可以與非大小範圍一起呼叫	const 過載需要 sized_range

另請參閱

end	返回一個迭代器或一個哨兵到末尾 (公共成員函式)
ranges::begin (C++20)	返回指向範圍開頭的迭代器 (定製點物件)
ranges::end (C++20)	返回指示範圍末尾的哨兵 (定製點物件)