std::counted_iterator<I>::counted_iterator

 

C++

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技术规范

 

迭代器库

迭代器概念
indirectly_readable (C++20) indirectly_writable (C++20) weakly_incrementable (C++20) incrementable (C++20) input_or_output_iterator (C++20) sentinel_for (C++20) sized_sentinel_for (C++20)	input_iterator (C++20) output_iterator (C++20) forward_iterator (C++20) bidirectional_iterator (C++20) random_access_iterator (C++20) contiguous_iterator (C++20)
迭代器原语
iterator_traits input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20) iterator (C++17 中弃用)	incrementable_traits (C++20) indirectly_readable_traits (C++20) iter_value_titer_difference_titer_reference_titer_rvalue_reference_titer_common_reference_t (C++20)(C++20)(C++20)(C++20)(C++20)
算法概念与工具
间接可调用概念
indirectly_unary_invocableindirectly_regular_unary_invocable (C++20)(C++20) indirect_unary_predicate (C++20)	indirect_binary_predicate (C++20) indirect_equivalence_relation (C++20) indirect_strict_weak_order (C++20)
常用算法要求
indirectly_movable (C++20) indirectly_movable_storable (C++20) indirectly_copyable (C++20) indirectly_copyable_storable (C++20)	indirectly_swappable (C++20) indirectly_comparable (C++20) permutable (C++20) mergeable (C++20) sortable (C++20)
工具
indirect_result_t	projected
迭代器适配器
reverse_iterator move_iterator (C++11) move_sentinel (C++20) common_iterator (C++20) counted_iterator (C++20) back_insert_iterator front_insert_iterator insert_iterator	make_reverse_iterator (C++14) make_move_iterator (C++11) default_sentinel_tdefault_sentinel (C++20)(C++20) unreachable_sentinel_tunreachable_sentinel (C++20)(C++20) back_inserter front_inserter inserter
流迭代器
istream_iterator ostream_iterator	istreambuf_iterator ostreambuf_iterator
迭代器定制点
ranges::iter_move (C++20)
ranges::iter_swap (C++20)
迭代器操作
advance distance prev (C++11) next (C++11)	ranges::advance (C++20) ranges::distance (C++20) ranges::prev (C++20) ranges::next (C++20)
范围访问
begincbegin (C++11)(C++14) endcend (C++11)(C++14) sizessize (C++17)(C++20)	rbegincrbegin (C++14)(C++14) rendcrend (C++14)(C++14) empty (C++17) data (C++17)

 

std::counted_iterator

成员函数

counted_iterator::counted_iterator (C++20)

counted_iterator::operator= (C++20)

counted_iterator::base (C++20)

counted_iterator::count (C++20)

counted_iterator::operator*counted_iterator::operator-> (C++20)(C++20)

counted_iterator::operator[] (C++20)

counted_iterator::operator++counted_iterator::operator++(int)counted_iterator::operator+counted_iterator::operator+=counted_iterator::operator--counted_iterator::operator--(int)counted_iterator::operator-counted_iterator::operator-= (C++20)(C++20)(C++20)(C++20)(C++20)(C++20)(C++20)(C++20)

非成员函数

operator==operator<=> (C++20)(C++20)

operator==(default_sentinel_t) (C++20)

operator+ (C++20)

operator- (C++20)

operator-(default_sentinel_t) (C++20)

iter_move (C++20)

iter_swap (C++20)

辅助类

iterator_traits (C++20)

 

constexpr counted_iterator() requires std::default_initializable<I> = default;	(1)	(C++20 起)
constexpr counted_iterator( I x, std::iter_difference_t<I> n );	(2)	(C++20 起)
template< class I2 >   requires std::convertible_to<const I2&, I>     constexpr counted_iterator( const counted_iterator<I2>& other );	(3)	(C++20 起)

构造新的迭代器适配器。

1) 默认构造函数。值初始化底层迭代器并以 ​0​ 初始化底层长度。在结果迭代器上的操作拥有有定义行为当且仅当值初始化的 I 上的对应操作亦拥有有定义行为。

2) 以 std::move(x) 初始化底层迭代器并以 n 初始化底层长度。若 n 为负则行为未定义。

3) 以 other 的对应组分初始化底层迭代器与长度。

参数

x	-	要适配的迭代器
n	-	到末尾的距离
other	-	要转换的迭代器适配器

示例

运行此代码

#include <algorithm>
#include <initializer_list>
#include <iostream>
#include <iterator>
 
int main() {
    static constexpr auto pi = {3, 1, 4, 1, 5, 9, 2};
 
    // (1) 默认构造函数：
    constexpr std::counted_iterator<std::initializer_list<int>::iterator> i1{};
    static_assert(i1 == std::default_sentinel);
    static_assert(i1.count() == 0);
 
    // (2) 分别初始化迭代器与长度：
    constexpr std::counted_iterator<std::initializer_list<int>::iterator> i2{
        pi.begin(), pi.size() - 2
    };
    static_assert(i2.count() == 5);
    static_assert(*i2 == 3 && i2[1] == 1);
 
    // (3) 转换构造函数：
    std::counted_iterator<std::initializer_list<const int>::iterator> i3{i2};
 
    std::ranges::copy(i3, std::default_sentinel,
        std::ostream_iterator<const int>{std::cout, " "});
}

输出：

3 1 4 1 5

参阅

operator= (C++20)

赋值另一迭代器适配器 (公开成员函数)