std::search() algorithm

od C++20

// (1)
template< class ForwardIt1, class ForwardIt2 >
constexpr ForwardIt1 search( ForwardIt1 first, ForwardIt1 last,
                   ForwardIt2 s_first, ForwardIt2 s_last );

// (2)
template< class ForwardIt1, class ForwardIt2, class BinaryPredicate >
constexpr ForwardIt1 search( ForwardIt1 first, ForwardIt1 last,
                   ForwardIt2 s_first, ForwardIt2 s_last,
                   BinaryPredicate p );

// (3)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2 >
ForwardIt1 search( ExecutionPolicy&& policy,
                   ForwardIt1 first, ForwardIt1 last,
                   ForwardIt2 s_first, ForwardIt2 s_last );

// (4)
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 );

// (5)
template< class ForwardIt, class Searcher >
constexpr ForwardIt search( ForwardIt first, ForwardIt last, const Searcher& searcher );

od C++17

// (1)
template< class ForwardIt1, class ForwardIt2 >
ForwardIt1 search( ForwardIt1 first, ForwardIt1 last,
                   ForwardIt2 s_first, ForwardIt2 s_last );

// (2)
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 >
ForwardIt1 search( ExecutionPolicy&& policy,
                   ForwardIt1 first, ForwardIt1 last,
                   ForwardIt2 s_first, ForwardIt2 s_last );

// (4)
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 );

// (5)
template< class ForwardIt, class Searcher >
ForwardIt search( ForwardIt first, ForwardIt last, const Searcher& searcher );

do C++17

// (1)
template< class ForwardIt1, class ForwardIt2 >
ForwardIt1 search( ForwardIt1 first, ForwardIt1 last,
                   ForwardIt2 s_first, ForwardIt2 s_last );

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

Searches for the first occurence of a range of elements inside another range.

• (1 - 4) Searches for the first occurrence of the sequence of elements [s_first; s_last) in the range [first; last):

  • (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.

    Overload Resolution

    These overloads participate in overload resolution only if std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>  (do C++20) std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>  (od C++20) is true.

• (5) Searches the sequence [first; last) for the pattern specified in the constructor of searcher. Effectively executes return searcher(first, last).first;.

  important

  Searcher cannot be CopyConstructible.

  The standard library provides the following searchers:

  od C++17

  default_searcher	Standard C++ library search algorithm implementation.
  boyer_moore_searcher	Boyer-Moore search algorithm implementation.
  boyer_moore_horspool_searcher	Boyer-Moore-Horspool search algorithm implementation.

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 function should be equivalent to the following: bool fun(const Type1& a, const Type2& b); The signature does not need to have const&. The function must not modify the objects passed to it Must accept all values of type (possibly const) Type and Type2, regardless of value category (so Type1& is not allowed, nor is Type1 unless for Type1 a move is equivalent to a copy (od C++11)) The types Type1 and Type2 must be such that an object of type ForwardIt1 and ForwardIt2 can be dereferenced and then implicitly converted to them.

Type requirements

ForwardIt1 ForwardIt2	LegacyForwardIterator
Searcher	Searcher

Return value

• (1 - 4) Iterator to the beginning of first occurrence of the sequence [s_first; s_last) in the range [first; last). If [s_first; s_last) is empty or if no such sequence is found, last is returned.  (od C++11)

  
  If no such sequence is found, last is returned.  (do C++11)

• (5) Returns the result of searcher's operator(), that is, an iterator to the location at which the substring is found or a copy of last if it was not found.

Complexity

(1 - 4) Given S as std::distance(s_first, s_last) and N as std::distance(first, last): At most S * N comparisons.

(5) Depends on the searcher. Standard searchers don't have a guaranteed complexity.

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 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.

Possible implementation

search (1)

template<class ForwardIt1, class ForwardIt2>
constexpr 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 BinaryPredicate>
constexpr ForwardIt1 search(ForwardIt1 first, ForwardIt1 last,
                            ForwardIt2 s_first, ForwardIt2 s_last,
                            BinaryPredicate 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;
    }
}

Examples

Main.cpp

#include <algorithm>
#include <functional>
#include <iomanip>
#include <iostream>
#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};

    std::cout << std::boolalpha
              << contains(str, "learning") << '\n'   // true
              << contains(str, "lemming")  << '\n';  // false

    const std::vector vec(str.begin(), str.end());
    std::cout << contains(vec, "learning") << '\n'   // true
              << contains(vec, "leaning")  << '\n';  // false

    // The C++17 overload with searchers demo:
    constexpr auto haystack
    {
        "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed "
        "do eiusmod tempor incididunt ut labore et dolore magna aliqua"sv
    };

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

Output

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