26 Algorithms library [algorithms]

26.6 Non-modifying sequence operations [alg.nonmodifying]

26.6.9 Find first [alg.find.first.of]

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template<class InputIterator, class ForwardIterator> constexpr InputIterator find_first_of(InputIterator first1, InputIterator last1, ForwardIterator first2, ForwardIterator last2); template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2> ForwardIterator1 find_first_of(ExecutionPolicy&& exec, ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2); template<class InputIterator, class ForwardIterator, class BinaryPredicate> constexpr InputIterator find_first_of(InputIterator first1, InputIterator last1, ForwardIterator first2, ForwardIterator last2, BinaryPredicate pred); template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2, class BinaryPredicate> ForwardIterator1 find_first_of(ExecutionPolicy&& exec, ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2, BinaryPredicate pred); template<input_iterator I1, sentinel_for<I1> S1, forward_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 I1 ranges::find_first_of(I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {}); template<input_range R1, forward_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 borrowed_iterator_t<R1> ranges::find_first_of(R1&& r1, R2&& r2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {});
1
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Let E be:
  • (1.1)
    *i == *j for the overloads with no parameter pred;
  • (1.2)
    pred(*i, *j) != false for the overloads with a parameter pred and no parameter proj1;
  • (1.3)
    bool(invoke(pred, invoke(proj1, *i), invoke(proj2, *j))) for the overloads with parameters pred and proj1.
2
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Effects: Finds an element that matches one of a set of values.
3
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Returns: The first iterator i in the range [first1, last1) such that for some iterator j in the range [first2, last2) E holds.
Returns last1 if [first2, last2) is empty or if no such iterator is found.
4
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Complexity: At most (last1-first1) * (last2-first2) applications of the corresponding predicate and any projections.