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cppdraft/unreachable/sentinel.md

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+[unreachable.sentinel]
+
+# 24 Iterators library [[iterators]](./#iterators)
+
+## 24.5 Iterator adaptors [[predef.iterators]](predef.iterators#unreachable.sentinel)
+
+### 24.5.8 Unreachable sentinel [unreachable.sentinel]
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L6449)
+
+Class unreachable_sentinel_t can be used with
+any [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") type
+to denote the “upper bound” of an unbounded interval[.](#1.sentence-1)
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L6454)
+
+[*Example [1](#example-1)*: char* p;// set p to point to a character buffer containing newlineschar* nl = find(p, unreachable_sentinel, '\n');
+
+Provided a newline character really exists in the buffer, the use ofunreachable_sentinel above potentially makes the call to find more
+efficient since the loop test against the sentinel does not require a
+conditional branch[.](#2.sentence-1)
+
+— *end example*]
+
+[🔗](#lib:operator==,unreachable_sentinel_t)
+
+namespace std {struct unreachable_sentinel_t {template<[weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") I>friend constexpr bool operator==(unreachable_sentinel_t, const I&) noexcept{ return false; }};}