std::unreachable_sentinel_t, std::unreachable_sentinel

 

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定义于头文件 <iterator>
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)