26 Algorithms library [algorithms]

26.6 Non-modifying sequence operations [alg.nonmodifying]

26.6.13 Equal [alg.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 I1, sentinel_for<I1> S1, input_iterator I2, sentinel_for<I2> S2,
         class Pred = ranges::equal_to, class Proj1 = identity, class Proj2 = identity>
  requires indirectly_comparable<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 R1, input_range R2, class Pred = ranges::equal_to,
         class Proj1 = identity, class Proj2 = identity>
  requires indirectly_comparable<iterator_t<R1>, iterator_t<R2>, Pred, Proj1, Proj2>
  constexpr bool ranges::equal(R1&& r1, R2&& r2, Pred pred = {},
                               Proj1 proj1 = {}, Proj2 proj2 = {});

Let:

(1.1)
last2 be first2 + (last1 - first1) for the overloads with no parameter last2 or r2;
(1.2)
pred be equal_to{} for the overloads with no parameter pred;
(1.3)
E be:
- (1.3.1)
  pred(*i, *(first2 + (i - first1))) for the overloads with no parameter proj1;
- (1.3.2)
  invoke(pred, invoke(proj1, *i), invoke(proj2, *(first2 + (i - first1)))) for the overloads with parameter proj1.

Returns: If last1 - first1 != last2 - first2, return false.

Otherwise return true if E holds for every iterator i in the range [first1, last1).

Otherwise, returns false.

Complexity: If

(3.1)
the types of first1, last1, first2, and last2 meet the Cpp17RandomAccessIterator requirements ([random.access.iterators]) and last1 - first1 != last2 - first2 for the overloads in namespace std;
(3.2)
the types of first1, last1, first2, and last2 pairwise model sized_sentinel_for ([iterator.concept.sizedsentinel]) and last1 - first1 != last2 - first2 for the first overload in namespace ranges,
(3.3)
R1 and R2 each model sized_range and ranges::distance(r1) != ranges::distance(r2) for the second overload in namespace ranges,

then no applications of the corresponding predicate and each projection; otherwise,

(3.4)
For the overloads with no ExecutionPolicy, at most min(last1 - first1, last2 - first2) applications of the corresponding predicate and any projections.
(3.5)
For the overloads with an ExecutionPolicy, $O (min (last1 - first1, last2 - first2))$ applications of the corresponding predicate.