# std::boyer_moore_searcher

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< cpp‎ | utility‎ | functional

Defined in header `<functional>` |  |
template< class RandomIt1, class Hash = std::hash<typename std::iterator_traits<RandomIt1>::value_type>, class BinaryPredicate = std::equal_to<> > class boyer_moore_searcher; |  | (since C++17)

A searcher suitable for use with the Searcher overload of std::search that implements the Boyer-Moore string searching algorithm.

`std::boyer_moore_searcher` is CopyConstructible and CopyAssignable.

`RandomIt1` must meet the requirements of LegacyRandomAccessIterator.

### Member functions

## std::boyer_moore_searcher::boyer_moore_searcher

boyer_moore_searcher( RandomIt1 pat_first, RandomIt1 pat_last, Hash hf = Hash(), BinaryPredicate pred = BinaryPredicate() ); |  |

Constructs a `std::boyer_moore_searcher` by storing copies of pat_first, pat_last, hf, and pred, setting up any necessary internal data structures.

The value type of `RandomIt1` must be DefaultConstructible, CopyConstructible and CopyAssignable.

For any two values `A` and `B` of the type std::iterator_traits<RandomIt1>::value_type, if pred(A, B) == true, then hf(A) == hf(B) shall be true.

### Parameters

pat_first, pat_last | - | a pair of iterators designating the string to be searched for
hf | - | a callable object used to hash the elements of the string
pred | - | a callable object used to determine equality

### Exceptions

Any exceptions thrown by

- the copy constructor of `RandomIt1`;
- the default constructor, copy constructor, and copy assignment operator of the value type of `RandomIt1`; or
- the copy constructor and function call operator of `BinaryPredicate` or `Hash`.

May also throw std::bad_alloc if additional memory required for internal data structures cannot be allocated.

## std::boyer_moore_searcher::operator()

template< class RandomIt2 > std::pair<RandomIt2, RandomIt2> operator()( RandomIt2 first, RandomIt2 last ) const; |  | (since C++17)

The member function called by the Searcher overload of std::search to perform a search with this searcher. `RandomIt2` must meet the requirements of LegacyRandomAccessIterator.

`RandomIt1` and `RandomIt2` must have the same value type.

### Parameters

first, last | - | a pair of iterators designating the string to be examined

### Return value

If the pattern `[`pat_first`,` pat_last`)` is empty, returns std::make_pair(first, first).

Otherwise, returns a pair of iterators to the first and one past last positions in `[`first`,` last`)` where a subsequence that compares equal to `[`pat_first`,` pat_last`)` as defined by pred is located, or std::make_pair(last, last) otherwise.

### Notes

Feature-test macro | Value | Std | Comment
--- | --- | --- | ---
`__cpp_lib_boyer_moore_searcher` | 201603L | (C++17) | searchers

### Example

Run this code

    #include <algorithm>
    #include <functional>
    #include <iomanip>
    #include <iostream>
    #include <string_view>

    int main()
    {
        constexpr std::string_view haystack =
            "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed "
            "do eiusmod tempor incididunt ut labore et dolore magna aliqua";

        const std::string_view needle{"pisci"};

        if (const auto it = std::search(haystack.begin(), haystack.end(),
                std::boyer_moore_searcher(needle.begin(), needle.end()));
            it != haystack.end()
        )
            std::cout << "The string " << std::quoted(needle) << " found at offset "
                      << it - haystack.begin() << '\n';
        else
            std::cout << "The string " << std::quoted(needle) << " not found\n";
    }

Output:

    The string "pisci" found at offset 43

### See also

search | searches for a range of elements (function template)
default_searcher (C++17) | standard C++ library search algorithm implementation (class template)
boyer_moore_horspool_searcher (C++17) | Boyer-Moore-Horspool search algorithm implementation (class template)

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