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std::unreachable_sentinel_t, std::unreachable_sentinel

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unreachable_sentinel_tunreachable_sentinel
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Defined in header <iterator>
struct unreachable_sentinel_t;
(1) (since C++20)
inline constexpr unreachable_sentinel_t unreachable_sentinel{};
(2) (since C++20)
1) unreachable_sentinel_t is an empty class type that can be used to denote the “upper bound” of an unbounded interval.
2) unreachable_sentinel is a constant of type unreachable_sentinel_t.

Contents

[edit] Non-member functions

operator==
(C++20)
compares an unreachable_sentinel_t with a value of any weakly_incrementable type
(function template)

operator==(std::unreachable_sentinel_t)

template<std::weakly_incrementable I>

friend constexpr bool operator==( unreachable_sentinel_t, const I& ) noexcept

{ return false; }
(since C++20)

unreachable_sentinel_t can be compared with any weakly_incrementable type and the result is always false.

This function template is not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when std::unreachable_sentinel_t is an associated class of the arguments.

[edit] Example

#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';
}

Output:

44

[edit] See also

a view consisting of a sequence generated by repeatedly incrementing an initial value
(class template) (customization point object) [edit]