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# std::search

From cppreference.com
< cpp‎ | algorithm

Defined in header `<algorithm>` |  |
template< class ForwardIt1, class ForwardIt2 > ForwardIt1 search( ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last ); | (1) |
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)
template< class ForwardIt1, class ForwardIt2, class BinaryPredicate > ForwardIt1 search( ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last, BinaryPredicate p ); | (3) |
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)
template<class ForwardIterator, class Searcher> ForwardIterator search( ForwardIterator first, ForwardIterator last, const Searcher& searcher ); | (5) | (since C++17)

1-4) Searches for the first occurrence of the subsequence of elements `[s_first, s_last)` in the range `[first, last - (s_last - s_first))`.
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) [edit]
boyer_moore_searcher (C++17) | Boyer-Moore search algorithm implementation (class template) [edit]
boyer_moore_horspool_searcher (C++17) | Boyer-Moore-Horspool search algorithm implementation (class template) [edit]
| (since C++17)

### [edit] 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); The signature does not need to have const &, but the function must not modify the objects passed to it. 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 `ForwardIterator`.
- `Searcher` must meet the requirements of `Searcher`.

### [edit] Return value

1-4) Iterator to the beginning of first subsequence `[s_first, s_last)` in the range `[first, last - (s_last - s_first))`. If no such subsequence 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.

### [edit] 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

### [edit] 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 three 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.

### [edit] Possible implementation

First version
    template<class ForwardIt1, class ForwardIt2>
    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>
    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;
                }
            }
        }
    }

### [edit] Example

Run this code

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

    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::make_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

### [edit] See also

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

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