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# std::boyer_moore_searcher

From cppreference.com
< 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.

`boyer_moore_searcher` is `CopyConstructible` and `CopyAssignable`.

`RandomIt1` must meet the requirements of `RandomAccessIterator`.

### [edit] 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 `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 `RandomAccessIterator`.

`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 `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 `make_pair(last, last)` otherwise.

### [edit] Example

Run this code

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

    int main()
    {
        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:

    The string pisci found at offset 43

### [edit] See also

search | searches for a range of elements (function template) [edit]

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