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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 ForwardIt1, class ForwardIt2, class BinaryPredicate > ForwardIt1 search( ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last, BinaryPredicate p ); | (2) |

Searches for the first occurrence of the subsequence of elements `[s_first, s_last)` in the range `[first, last - (s_last - s_first))`. The first version uses `operator==` to compare the elements, the second version uses the given binary predicate `p`.

### [edit] Parameters

first, last | - | the range of elements to examine
s_first, s_last | - | the range of elements to search 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`.

### [edit] Return value

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)

### [edit] Complexity

At most `S*N` comparisons where S = std::distance(s_first, s_last) and N = std::distance(first, last).

### [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>

    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';
    }

Output:

    true
    false
    true
    false

### [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]
find find_if find_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]

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