88 lines
2.7 KiB
Markdown
88 lines
2.7 KiB
Markdown
[iterator.operations]
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# 24 Iterators library [[iterators]](./#iterators)
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## 24.4 Iterator primitives [[iterator.primitives]](iterator.primitives#iterator.operations)
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### 24.4.3 Iterator operations [iterator.operations]
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[1](#1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L2834)
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Since only random access iterators provide+ and- operators, the library provides two
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function templatesadvance anddistance[.](#1.sentence-1)
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These
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function templates
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use+ and- for random access iterators (and are, therefore, constant
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time for them); for input, forward and bidirectional iterators they use++ to provide linear time
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implementations[.](#1.sentence-2)
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[ð](#lib:advance)
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`template<class InputIterator, class Distance>
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constexpr void advance(InputIterator& i, Distance n);
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`
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[2](#2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L2863)
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*Preconditions*: n is negative only for bidirectional iterators[.](#2.sentence-1)
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[3](#3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L2868)
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*Effects*: Increments i by n if n is non-negative, and
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decrements i by -n otherwise[.](#3.sentence-1)
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[ð](#lib:distance)
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`template<class InputIterator>
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constexpr typename iterator_traits<InputIterator>::difference_type
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distance(InputIterator first, InputIterator last);
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`
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[4](#4)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L2882)
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*Preconditions*: last is reachable from first, orInputIterator meets
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the *Cpp17RandomAccessIterator* requirements andfirst is reachable from last[.](#4.sentence-1)
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[5](#5)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L2889)
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*Effects*: If InputIterator meets the *Cpp17RandomAccessIterator* requirements,
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returns (last - first); otherwise, incrementsfirst until last is reached and returns
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the number of increments[.](#5.sentence-1)
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[ð](#lib:next)
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`template<class InputIterator>
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constexpr InputIterator next(InputIterator x,
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typename iterator_traits<InputIterator>::difference_type n = 1);
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`
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[6](#6)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L2905)
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*Effects*: Equivalent to: advance(x, n); return x;
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[ð](#lib:prev)
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`template<class BidirectionalIterator>
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constexpr BidirectionalIterator prev(BidirectionalIterator x,
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typename iterator_traits<BidirectionalIterator>::difference_type n = 1);
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`
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[7](#7)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L2918)
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*Effects*: Equivalent to: advance(x, -n); return x;
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