Namespaces
Variants

    std::search

    From cppreference.com
     
    C++
     
    Algorithm library
    Constrained algorithms and algorithms on ranges (C++20)
    Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
    Non-modifying sequence operations    
    Batch operations
    (C++17)
    Search operations
    Modifying sequence operations
    Copy operations
    (C++11)
    (C++11)
    (C++11)
    Swap operations
    Transformation operations
    Generation operations
    Removing operations
    Order-changing operations
    (until C++17)(C++11)
    (C++20)(C++20)
    Sampling operations
    (C++17)

    Sorting and related operations
    Partitioning operations
    (C++11)    
    (C++11)

    Sorting operations
    Binary search operations
    (on partitioned ranges)
    Set operations (on sorted ranges)
    Merge operations (on sorted ranges)
    Heap operations
    Minimum/maximum operations
    (C++11)
    (C++17)
    Lexicographical comparison operations
    (C++20)
    Permutation operations


     
    Defined in header <algorithm> 
    template< class ForwardIt1, class ForwardIt2 >
ForwardIt1 search( ForwardIt1 first1, ForwardIt1 last1,
                   ForwardIt2 first2, ForwardIt2 last2 );
    		(1) (constexpr since C++20) 
    template< class ForwardIt1, class ForwardIt2, class BinaryPred >
ForwardIt1 search( ForwardIt1 first1, ForwardIt1 last1,
                   ForwardIt2 first2, ForwardIt2 last2,
                   BinaryPred p );
    		(2) (constexpr since C++20) 
    template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2 >
ForwardIt1 search( ExecutionPolicy&& policy,
                   ForwardIt1 first1, ForwardIt1 last1,
                   ForwardIt2 first2, ForwardIt2 last2 );
    		(3) (since C++17) 
    template< class ExecutionPolicy,
          class ForwardIt1, class ForwardIt2, class BinaryPred >
ForwardIt1 search( ExecutionPolicy&& policy,
                   ForwardIt1 first1, ForwardIt1 last1,
                   ForwardIt2 first2, ForwardIt2 last2,
                   BinaryPred p );
    		(4) (since C++17) 
    template< class ForwardIt, class Searcher >
ForwardIt search( ForwardIt first1, ForwardIt last1,
                  const Searcher& searcher );
    		(5) (since C++17)
    1-4) Searches for the first occurrence of the target range [first2, last2) in the source range [first1, last1).
    1) Elements are compared using operator==.
    2) Elements are compared using the given binary predicate p.
    3,4) Same as (1,2), but executed according to policy.
    These overloads participate in overload resolution only if the value of the following expression is true:

    std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>

    		(until C++20)

    std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>

    		(since C++20)
    5) Searches the source range [first1, last1) using searcher. The target range is generally provided during the construction of searcher.
    The standard library provides the following searchers:
    (C++17)
    		 standard C++ library search algorithm implementation
    (class template) [edit]
    (C++17)
    		 Boyer-Moore search algorithm implementation
    (class template) [edit]
    (C++17)
    		 Boyer-Moore-Horspool search algorithm implementation
    (class template) [edit]

    Parameters

    first1, last1 - the pair of iterators defining the source range
    first2, last2 - the pair of iterators defining the target range
    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. ​

    policy - the execution policy to use
    searcher - the searcher encapsulating the search algorithm and the pattern to look for
    Type requirements
    -
    ForwardIt1, ForwardIt2 must meet the requirements of LegacyForwardIterator.
    -
    BinaryPred must meet the requirements of BinaryPredicate.

    Return value

    1-4) Iterator to the beginning of the first occurrence of the target range in source range.
    • If the target range is empty, first1 is returned.
    • If the target range does not appear in the source range, last1 is returned.
    5) searcher(first, last).first

    Complexity

    Given N1 as std::distance(first1, last1) and N2 as std::distance(first2, last2):

    1) At most N1⋅N2 comparisons using operator==.
    2) At most N1⋅N2 applications of p.
    3) 𝓞(N1⋅N2) comparisons using operator==.
    4) 𝓞(N1⋅N2) applications of p.
    5) Depends on searcher.

    Exceptions

    3,4) During the execution process:
    • If the temporary memory resources required for parallelization are not available, std::bad_alloc is thrown.
    • If an uncaught exception is thrown while accessing objects via an algorithm argument, the behavior is determined by the execution policy (for standard policies, std::terminate is invoked).

    Possible implementation

    search (1) 
    template<class ForwardIt1, class ForwardIt2>
constexpr //< since C++20
ForwardIt1 search(ForwardIt1 first, ForwardIt1 last,
                  ForwardIt2 s_first, ForwardIt2 s_last)
{
    while (true)
    {
        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;
        }
        ++first;
    }
}
    search (2) 
    template<class ForwardIt1, class ForwardIt2, class BinaryPred>
constexpr //< since C++20
ForwardIt1 search(ForwardIt1 first, ForwardIt1 last,
                  ForwardIt2 s_first, ForwardIt2 s_last, BinaryPred p)
{
    while (true)
    {
        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;
        }
        ++first;
    }
}

    Example

    Run this code
    #include <algorithm>
#include <cassert>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <string_view>
#include <vector>

using namespace std::literals;

bool contains(const auto& cont, std::string_view s)
{
    // str.find() (or str.contains(), since C++23) can be used as well
    return std::search(cont.begin(), cont.end(), s.begin(), s.end()) != cont.end();
}

int main()
{
    const auto str{"why waste time learning, when ignorance is instantaneous?"sv};
    assert(contains(str, "learning"));
    assert(not contains(str, "lemming"));
    
    const std::vector vec(str.begin(), str.end());
    assert(contains(vec, "learning"));
    assert(not contains(vec, "leaning"));
    
    // The C++17 overload with searchers demo:
    constexpr auto quote
    {
        "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed "
        "do eiusmod tempor incididunt ut labore et dolore magna aliqua"sv
    };
    
    for (const auto word : {"pisci"sv, "Pisci"sv})
    {
        std::cout << "The string " << std::quoted(word) << ' ';
        const std::boyer_moore_searcher searcher(word.begin(), word.end());
        const auto it = std::search(quote.begin(), quote.end(), searcher);
        if (it == quote.end())
            std::cout << "not found\n";
        else
            std::cout << "found at offset " << std::distance(quote.begin(), it) << '\n';
    }
}

    Output: 

    The string "pisci" found at offset 43
The string "Pisci" not found

    Defect reports

    The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

    DR Applied to Behavior as published Correct behavior
    LWG 1205 C++98 the return value was unclear if the target range is empty returns first1 in this case
    LWG 1338 C++98 the resolution of LWG issue 1205 was incorrectly applied,
    making first1 to be returned if the target range is not found     		returns last1 in this case
    LWG 2150 C++98 the condition of “sequence occurence” was incorrect corrected

    See also

    (C++20)
    		 searches for the first occurrence of a range of elements
    (algorithm function object)[edit]
    		searches for the first occurrence of a number consecutive copies of an element in a range
    (function template & algorithm function object)[edit]
    (C++20)
    		finds the last sequence of elements in a certain range
    (function template & algorithm function object)[edit]
    (C++20)
    		determines if one sequence is a subsequence of another
    (function template & algorithm function object)[edit]
    (C++20)
    		determines if two sets of elements are the same
    (function template & algorithm function object)[edit]
    (C++20)
    (C++11)
    		 finds the first element satisfying specific criteria
    (function template & algorithm function object)[edit]
    (C++20)(C++20)(C++20)
    		compares two ranges lexicographically
    (function template & algorithm function object)[edit]
    (C++20)
    		finds the first position where two ranges differ
    (function template & algorithm function object)[edit]
    (C++20)