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[alg.equal]
# 26 Algorithms library [[algorithms]](./#algorithms)
## 26.6 Non-modifying sequence operations [[alg.nonmodifying]](alg.nonmodifying#alg.equal)
### 26.6.13 Equal [alg.equal]
[🔗](#lib:equal)
`template<class InputIterator1, class InputIterator2>
constexpr bool equal(InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2);
template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2>
bool equal(ExecutionPolicy&& exec,
ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2);
template<class InputIterator1, class InputIterator2,
class BinaryPredicate>
constexpr bool equal(InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, BinaryPredicate pred);
template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2,
class BinaryPredicate>
bool equal(ExecutionPolicy&& exec,
ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, BinaryPredicate pred);
template<class InputIterator1, class InputIterator2>
constexpr bool equal(InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2);
template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2>
bool equal(ExecutionPolicy&& exec,
ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2);
template<class InputIterator1, class InputIterator2,
class BinaryPredicate>
constexpr bool equal(InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
BinaryPredicate pred);
template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2,
class BinaryPredicate>
bool equal(ExecutionPolicy&& exec,
ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2,
BinaryPredicate pred);
template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9Concept input_­iterator[iterator.concept.input]") I1, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7Concept sentinel_­for[iterator.concept.sentinel]")<I1> S1, [input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9Concept input_­iterator[iterator.concept.input]") I2, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7Concept sentinel_­for[iterator.concept.sentinel]")<I2> S2,
class Pred = ranges::equal_to, class Proj1 = identity, class Proj2 = identity>
requires [indirectly_comparable](alg.req.ind.cmp#concept:indirectly_comparable "24.3.7.5Concept indirectly_­comparable[alg.req.ind.cmp]")<I1, I2, Pred, Proj1, Proj2>
constexpr bool ranges::equal(I1 first1, S1 last1, I2 first2, S2 last2,
Pred pred = {},
Proj1 proj1 = {}, Proj2 proj2 = {});
template<[input_range](range.refinements#concept:input_range "25.4.6Other range refinements[range.refinements]") R1, [input_range](range.refinements#concept:input_range "25.4.6Other range refinements[range.refinements]") R2, class Pred = ranges::equal_to,
class Proj1 = identity, class Proj2 = identity>
requires [indirectly_comparable](alg.req.ind.cmp#concept:indirectly_comparable "24.3.7.5Concept indirectly_­comparable[alg.req.ind.cmp]")<iterator_t<R1>, iterator_t<R2>, Pred, Proj1, Proj2>
constexpr bool ranges::equal(R1&& r1, R2&& r2, Pred pred = {},
Proj1 proj1 = {}, Proj2 proj2 = {});
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1Preamble[algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13Concept random_­access_­iterator[iterator.concept.random.access]") I1, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8Concept sized_­sentinel_­for[iterator.concept.sizedsentinel]")<I1> S1,
[random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13Concept random_­access_­iterator[iterator.concept.random.access]") I2, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8Concept sized_­sentinel_­for[iterator.concept.sizedsentinel]")<I2> S2,
class Pred = ranges::equal_to, class Proj1 = identity, class Proj2 = identity>
requires [indirectly_comparable](alg.req.ind.cmp#concept:indirectly_comparable "24.3.7.5Concept indirectly_­comparable[alg.req.ind.cmp]")<I1, I2, Pred, Proj1, Proj2>
bool ranges::equal(Ep&& exec, I1 first1, S1 last1, I2 first2, S2 last2,
Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {});
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1Preamble[algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6Other range refinements[range.refinements]") R1, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6Other range refinements[range.refinements]") R2,
class Pred = ranges::equal_to, class Proj1 = identity, class Proj2 = identity>
requires [indirectly_comparable](alg.req.ind.cmp#concept:indirectly_comparable "24.3.7.5Concept indirectly_­comparable[alg.req.ind.cmp]")<iterator_t<R1>, iterator_t<R2>, Pred, Proj1, Proj2>
bool ranges::equal(Ep&& exec, R1&& r1, R2&& r2,
Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {});
`
[1](#1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L5645)
Let:
- [(1.1)](#1.1)
last2 be first2 + (last1 - first1) for the overloads in namespace std with no parameter last2;
- [(1.2)](#1.2)
pred be equal_to{} for the overloads with no parameter pred;
- [(1.3)](#1.3)
E be:
* [(1.3.1)](#1.3.1)
pred(*i, *(first2 + (i - first1))) for the overloads with no parameter proj1;
* [(1.3.2)](#1.3.2)
invoke(pred, invoke(proj1, *i), invoke(proj2, *(first2 + (i - first1)))) for the overloads with parameter proj1[.](#1.sentence-1)
[2](#2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L5667)
*Returns*: If last1 - first1 != last2 - first2, return false[.](#2.sentence-1)
Otherwise return true if E holds for every iterator i in the range [first1, last1)[.](#2.sentence-2)
Otherwise, returns false[.](#2.sentence-3)
[3](#3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L5674)
*Complexity*: If
- [(3.1)](#3.1)
the types of first1, last1, first2, and last2 meet the [*Cpp17RandomAccessIterator*](random.access.iterators#:Cpp17RandomAccessIterator "24.3.5.7Random access iterators[random.access.iterators]") requirements ([[random.access.iterators]](random.access.iterators "24.3.5.7Random access iterators"))
and last1 - first1 != last2 - first2 for the overloads in namespace std;
- [(3.2)](#3.2)
the types of first1, last1, first2, and last2 pairwise model [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8Concept sized_­sentinel_­for[iterator.concept.sizedsentinel]") ([[iterator.concept.sizedsentinel]](iterator.concept.sizedsentinel "24.3.4.8Concept sized_­sentinel_­for"))
and last1 - first1 != last2 - first2 for the first and third overloads in namespace ranges, or
- [(3.3)](#3.3)
R1 and R2 each model [sized_range](range.sized#concept:sized_range "25.4.4Sized ranges[range.sized]") and ranges::distance(r1) != ranges::distance(r2) for the second and fourth overloads in namespace ranges,
then no applications of the corresponding predicate and each projection;
otherwise, at most min(last1 - first1, last2 - first2) applications of the corresponding predicate and any projections[.](#3.sentence-1)