# 27 Algorithms library [algorithms]

## 27.6 Non-modifying sequence operations [alg.nonmodifying]

### 27.6.15 Search [alg.search]

```template<class ForwardIterator1, class ForwardIterator2> constexpr ForwardIterator1 search(ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2); template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2> ForwardIterator1 search(ExecutionPolicy&& exec, ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2); template<class ForwardIterator1, class ForwardIterator2, class BinaryPredicate> constexpr ForwardIterator1 search(ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2, BinaryPredicate pred); template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2, class BinaryPredicate> ForwardIterator1 search(ExecutionPolicy&& exec, ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2, BinaryPredicate pred); ```
Returns: The first iterator i in the range [first1, last1 - (last2-first2)) such that for every non-negative integer n less than last2 - first2 the following corresponding conditions hold: *(i + n) == *(first2 + n), pred(*(i + n), *(first2 + n)) != false.
Returns first1 if [first2, last2) is empty, otherwise returns last1 if no such iterator is found.
Complexity: At most (last1 - first1) * (last2 - first2) applications of the corresponding predicate.
```template<forward_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 subrange<I1> ranges::search(I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {}); template<forward_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_subrange_t<R1> ranges::search(R1&& r1, R2&& r2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {}); ```
Returns:
• {i, i + (last2 - first2)}, where i is the first iterator in the range [first1, last1 - (last2 - first2)) such that for every non-negative integer n less than last2 - first2 the condition bool(invoke(pred, invoke(proj1, *(i + n)), invoke(proj2, *(first2 + n)))) is true.
• Returns {last1, last1} if no such iterator exists.
Complexity: At most (last1 - first1) * (last2 - first2) applications of the corresponding predicate and projections.
```template<class ForwardIterator, class Size, class T = iterator_traits<ForwardIterator>::value_type> constexpr ForwardIterator search_n(ForwardIterator first, ForwardIterator last, Size count, const T& value); template<class ExecutionPolicy, class ForwardIterator, class Size, class T = iterator_traits<ForwardIterator>::value_type> ForwardIterator search_n(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last, Size count, const T& value); template<class ForwardIterator, class Size, class T = iterator_traits<ForwardIterator>::value_type, class BinaryPredicate> constexpr ForwardIterator search_n(ForwardIterator first, ForwardIterator last, Size count, const T& value, BinaryPredicate pred); template<class ExecutionPolicy, class ForwardIterator, class Size, class T = iterator_traits<ForwardIterator>::value_type, class BinaryPredicate> ForwardIterator search_n(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last, Size count, const T& value, BinaryPredicate pred); ```
Mandates: The type Size is convertible to an integral type ([conv.integral], [class.conv]).
Let E be pred(*(i + n), value) != false for the overloads with a parameter pred, and *(i + n) == value otherwise.
Returns: The first iterator i in the range [first, last-count) such that for every non-negative integer n less than count the condition E is true.
Returns last if no such iterator is found.
Complexity: At most last - first applications of the corresponding predicate.
```template<forward_iterator I, sentinel_for<I> S, class Pred = ranges::equal_to, class Proj = identity, class T = projected_value_t<I, Proj>> requires indirectly_comparable<I, const T*, Pred, Proj> constexpr subrange<I> ranges::search_n(I first, S last, iter_difference_t<I> count, const T& value, Pred pred = {}, Proj proj = {}); template<forward_range R, class Pred = ranges::equal_to, class Proj = identity, class T = projected_value_t<iterator_t<R>, Proj>> requires indirectly_comparable<iterator_t<R>, const T*, Pred, Proj> constexpr borrowed_subrange_t<R> ranges::search_n(R&& r, range_difference_t<R> count, const T& value, Pred pred = {}, Proj proj = {}); ```
Returns: {i, i + count} where i is the first iterator in the range [first, last - count) such that for every non-negative integer n less than count, the following condition holds: invoke(pred, invoke(proj, *(i + n)), value).
Returns {last, last} if no such iterator is found.
Complexity: At most last - first applications of the corresponding predicate and projection.
```template<class ForwardIterator, class Searcher> constexpr ForwardIterator search(ForwardIterator first, ForwardIterator last, const Searcher& searcher); ```
Effects: Equivalent to: return searcher(first, last).first;
Remarks: Searcher need not meet the Cpp17CopyConstructible requirements.