# std::search

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< cpp‎ | algorithm

Defined in header `<algorithm>` |  |
| (1) |
template< class ForwardIt1, class ForwardIt2 > ForwardIt1 search( ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last ); |  | (until C++20)
template< class ForwardIt1, class ForwardIt2 > constexpr ForwardIt1 search( ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last ); |  | (since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2 > ForwardIt1 search( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last ); | (2) | (since C++17)
| (3) |
template< class ForwardIt1, class ForwardIt2, class BinaryPredicate > ForwardIt1 search( ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last, BinaryPredicate p ); |  | (until C++20)
template< class ForwardIt1, class ForwardIt2, class BinaryPredicate > constexpr ForwardIt1 search( ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last, BinaryPredicate p ); |  | (since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class BinaryPredicate > ForwardIt1 search( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last, BinaryPredicate p ); | (4) | (since C++17)
| (5) |
template<class ForwardIt, class Searcher> ForwardIt search( ForwardIt first, ForwardIt last, const Searcher& searcher ); |  | (since C++17) (until C++20)
template<class ForwardIt, class Searcher> constexpr ForwardIt search( ForwardIt first, ForwardIt last, const Searcher& searcher ); |  | (since C++20)

1-4) Searches for the first occurrence of the sequence of elements `[s_first, s_last)` in the range `[first, last)`.
1) Elements are compared using `operator==`.
3) Elements are compared using the given binary predicate `p`.
2,4) Same as (1,3), but executed according to `policy`. These overloads do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true
5) Searches the sequence [first, last) for the pattern specified in the constructor of `searcher`. Effectively executes return searcher(first, last).first;. `Searcher` need not be CopyConstructible.

The standard library provides the following searchers:

default_searcher (C++17) | standard C++ library search algorithm implementation (class template)
boyer_moore_searcher (C++17) | Boyer-Moore search algorithm implementation (class template)
boyer_moore_horspool_searcher (C++17) | Boyer-Moore-Horspool search algorithm implementation (class template)

(since C++17)

### Parameters

first, last | - | the range of elements to examine
s_first, s_last | - | the range of elements to search for
policy | - | the execution policy to use. See execution policy for details.
searcher | - | the searcher encapsulating the search algorithm and the pattern to look for

p

-

binary predicate which returns ​true if the elements should be treated as equal.

The signature of the predicate function should be equivalent to the following:

bool pred(const Type1 &a, const Type2 &b);

While the signature does not need to have const &, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) `Type1` and `Type2` regardless of value category (thus, Type1 & is not allowed, nor is Type1 unless for `Type1` a move is equivalent to a copy (since C++11)).
The types Type1 and Type2 must be such that objects of types ForwardIt1 and ForwardIt2 can be dereferenced and then implicitly converted to Type1 and Type2 respectively. ​

Type requirements
- `ForwardIt1, ForwardIt2` must meet the requirements of LegacyForwardIterator.
- `Searcher` must meet the requirements of Searcher.

### Return value

1-4) Iterator to the beginning of first occurrence of the sequence `[s_first, s_last)` in the range `[first, last)`. If no such occurrence is found, `last` is returned.
If `[s_first, s_last)` is empty, `first` is returned. (since C++11)
5) Returns the result of `searcher.operator()`, that is, an iterator to the location at which the substring is found or a copy of `last` if it was not found.

### Complexity

1-4) At most `S*N` comparisons where S = std::distance(s_first, s_last) and N = std::distance(first, last).
5) Depends on the searcher

### Exceptions

The overloads with a template parameter named `ExecutionPolicy` report errors as follows:

- If execution of a function invoked as part of the algorithm throws an exception and `ExecutionPolicy` is one of the standard policies, std::terminate is called. For any other `ExecutionPolicy`, the behavior is implementation-defined.
- If the algorithm fails to allocate memory, std::bad_alloc is thrown.

### Possible implementation

First version

    template<class ForwardIt1, class ForwardIt2>
    constexpr ForwardIt1 search(ForwardIt1 first, ForwardIt1 last,
                                ForwardIt2 s_first, ForwardIt2 s_last)
    {
        for (; ; ++first) {
            ForwardIt1 it = first;
            for (ForwardIt2 s_it = s_first; ; ++it, ++s_it) {
                if (s_it == s_last) {
                    return first;
                }
                if (it == last) {
                    return last;
                }
                if (!(*it == *s_it)) {
                    break;
                }
            }
        }
    }

Second version

    template<class ForwardIt1, class ForwardIt2, class BinaryPredicate>
    constexpr ForwardIt1 search(ForwardIt1 first, ForwardIt1 last,
                                ForwardIt2 s_first, ForwardIt2 s_last,
                                BinaryPredicate p)
    {
        for (; ; ++first) {
            ForwardIt1 it = first;
            for (ForwardIt2 s_it = s_first; ; ++it, ++s_it) {
                if (s_it == s_last) {
                    return first;
                }
                if (it == last) {
                    return last;
                }
                if (!p(*it, *s_it)) {
                    break;
                }
            }
        }
    }

### Example

Run this code

    #include <string>
    #include <algorithm>
    #include <iostream>
    #include <vector>
    #include <functional>

    template <typename Container>
    bool in_quote(const Container& cont, const std::string& s)
    {
        return std::search(cont.begin(), cont.end(), s.begin(), s.end()) != cont.end();
    }

    int main()
    {
        std::string str = "why waste time learning, when ignorance is instantaneous?";
        // str.find() can be used as well
        std::cout << std::boolalpha << in_quote(str, "learning") << '\n'
                                    << in_quote(str, "lemming")  << '\n';

        std::vector<char> vec(str.begin(), str.end());
        std::cout << std::boolalpha << in_quote(vec, "learning") << '\n'
                                    << in_quote(vec, "lemming")  << '\n';

        // The C++17 overload demo:
        std::string in = "Lorem ipsum dolor sit amet, consectetur adipiscing elit,"
                         " sed do eiusmod tempor incididunt ut labore et dolore magna aliqua";
        std::string needle = "pisci";
        auto it = std::search(in.begin(), in.end(),
                       std::boyer_moore_searcher(
                          needle.begin(), needle.end()));
        if(it != in.end())
            std::cout << "The string " << needle << " found at offset "
                      << it - in.begin() << '\n';
        else
            std::cout << "The string " << needle << " not found\n";
    }

Output:

    true
    false
    true
    false
    The string pisci found at offset 43

### See also

find_end | finds the last sequence of elements in a certain range (function template)
includes | returns true if one set is a subset of another (function template)
equal | determines if two sets of elements are the same (function template)
find find_if find_if_not (C++11) | finds the first element satisfying specific criteria (function template)
lexicographical_compare | returns true if one range is lexicographically less than another (function template)
mismatch | finds the first position where two ranges differ (function template)
search_n | searches a range for a number of consecutive copies of an element (function template)
default_searcher (C++17) | standard C++ library search algorithm implementation (class template)
boyer_moore_searcher (C++17) | Boyer-Moore search algorithm implementation (class template)
boyer_moore_horspool_searcher (C++17) | Boyer-Moore-Horspool search algorithm implementation (class template)

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