std::unreachable_sentinel_t, std::unreachable_sentinel

 

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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)
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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)
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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)
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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)
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indirect_result_t	projected
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reverse_iterator move_iterator (C++11) move_sentinel (C++20) common_iterator (C++20) counted_iterator (C++20) basic_const_iterator (C++23) const_iterator (C++23) const_sentinel (C++23) 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) make_const_iterator (C++23) make_const_sentinel (C++23) back_inserter front_inserter inserter
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istream_iterator ostream_iterator	istreambuf_iterator ostreambuf_iterator
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advance distance prev (C++11) next (C++11)	ranges::advance (C++20) ranges::distance (C++20) ranges::prev (C++20) ranges::next (C++20)
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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)

 

在标头 <iterator> 定义
struct unreachable_sentinel_t;	(1)	(C++20 起)
inline constexpr unreachable_sentinel_t unreachable_sentinel{};	(2)	(C++20 起)

1) unreachable_sentinel_t 是能用于表示无界区间“上界”的空类类型。

2) unreachable_sentinel 是 unreachable_sentinel_t 类型常量。

非成员函数

operator== (C++20)

比较一个 unreachable_sentinel_t 与任何 weakly_incrementable 类型值 (函数模板)

operator==(std::unreachable_sentinel_t)

template<std::weakly_incrementable I> friend constexpr bool operator==( unreachable_sentinel_t, const I& ) noexcept { return false; }		(C++20 起)

unreachable_sentinel_t 能与任何 weakly_incrementable 类型比较，而结果始终为 false 。

此函数模板对通常无限定或有限定查找不可见，而只能在 std::unreachable_sentinel_t 为参数的关联类时由实参依赖查找找到。

示例

运行此代码

#include <cstddef>
#include <iterator>
#include <algorithm>
#include <iostream>
 
template<class CharT>
std::size_t ntcts_len(const CharT *s)
{
    return std::ranges::find(s, std::unreachable_sentinel, CharT{}) - s;
}
 
int main()
{
    std::cout
        << ntcts_len("The quick brown fox jumps over the lazy dog.") << '\n';
}

输出：

44

参阅

ranges::iota_viewviews::iota (C++20)

由通过重复对某个初值自增所生成的序列组成的 view (类模板) (定制点对象)