25 Algorithms library [algorithms]

25.6 Non-modifying sequence operations [alg.nonmodifying]

25.6.11 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:
  • last2 be first2 + (last1 - first1) for the overloads with no parameter last2 or r2;
  • pred be equal_­to{} for the overloads with no parameter pred;
  • E be:
    • pred(*i, *(first2 + (i - first1))) for the overloads with no parameter proj1;
    • 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
  • 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;
  • 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,
  • 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,
  • For the overloads with no ExecutionPolicy, at most applications of the corresponding predicate and any projections.
  • For the overloads with an ExecutionPolicy, applications of the corresponding predicate.