[common.iter.cmp]

# 24 Iterators library [[iterators]](./#iterators)

## 24.5 Iterator adaptors [[predef.iterators]](predef.iterators#common.iter.cmp)

### 24.5.5 Common iterators [[iterators.common]](iterators.common#common.iter.cmp)

#### 24.5.5.6 Comparisons [common.iter.cmp]

[🔗](#lib:operator==,common_iterator)

`template<class I2, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S2>
  requires [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<S, I2>
friend constexpr bool operator==(
  const common_iterator& x, const common_iterator<I2, S2>& y);
`

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L5767)

*Hardened preconditions*: x.v_.valueless_by_exception() and y.v_.valueless_by_exception() are each false[.](#1.sentence-1)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L5772)

*Returns*: true if i == j,
and otherwise get<i>(x.v_) == get<j>(y.v_),
where i is x.v_.index() and j is y.v_.index()[.](#2.sentence-1)

[🔗](#lib:operator==,common_iterator_)

`template<class I2, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S2>
  requires [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<S, I2> && [equality_comparable_with](concept.equalitycomparable#concept:equality_comparable_with "18.5.4 Concept equality_­comparable [concept.equalitycomparable]")<I, I2>
friend constexpr bool operator==(
  const common_iterator& x, const common_iterator<I2, S2>& y);
`

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L5788)

*Hardened preconditions*: x.v_.valueless_by_exception() and y.v_.valueless_by_exception() are each false[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L5793)

*Returns*: true if i and j are each 1, and otherwiseget<i>(x.v_) == get<j>(y.v_), wherei is x.v_.index() and j is y.v_.index()[.](#4.sentence-1)

[🔗](#lib:operator-,common_iterator)

`template<[sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> I2, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S2>
  requires [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<S, I2>
friend constexpr iter_difference_t<I2> operator-(
  const common_iterator& x, const common_iterator<I2, S2>& y);
`

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L5809)

*Hardened preconditions*: x.v_.valueless_by_exception() and y.v_.valueless_by_exception() are each false[.](#5.sentence-1)

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L5814)

*Returns*: 0 if i and j are each 1, and otherwiseget<i>(x.v_) - get<j>(y.v_), wherei is x.v_.index() and j is y.v_.index()[.](#6.sentence-1)