std::search

class ForwardIt1, class ForwardIt2, class BinaryPred >
ForwardIt1 search( ExecutionPolicy&& policy,
ForwardIt1 first, ForwardIt1 last,
ForwardIt2 s_first, ForwardIt2 s_last,

BinaryPred p );

(4) (since C++17)

template< class ForwardIt, class Searcher >

ForwardIt search( ForwardIt first, ForwardIt last,

const Searcher& searcher );

(5) (since C++17)
(constexpr since C++20)

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==.

3) Elements are compared using the given binary predicate p.

2,4) Same as (1,3), but executed according to policy.

These overloads participate in overload resolution only if all following conditions are satisfied:

std::is_execution_policy_v <std::decay_t <ExecutionPolicy>> is true.

(until C++20)

std::is_execution_policy_v <std::remove_cvref_t <ExecutionPolicy>> is true.

(since C++20)

5) Searches the range [first, last) for the pattern specified in the constructor of searcher.

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)

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.

Type requirements

-ForwardIt1, ForwardIt2 must meet the requirements of LegacyForwardIterator.

-BinaryPred must meet the requirements of BinaryPredicate.

[edit] Return value

1-4) Iterator to the beginning of first occurrence of the sequence [s_first, s_last) in the range [first, last). If no such occurrence is found, last is returned.

If [s_first, s_last) is empty, first is returned.

5) searcher(first, last).first.

[edit] Complexity

1-4) Given \(\scriptsize N\)N as std::distance (first, last) and \(\scriptsize S\)S as std::distance (s_first, s_last):

1,2) At most \(\scriptsize N\cdot S\)N·S comparisons using operator==.

3,4) At most \(\scriptsize N\cdot S\)N·S applications of the predicate p.

5) Depends on 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 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

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 (3)

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;
 }
}

[edit] 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

[edit] 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 `[`s_first`,` s_last`)` is empty	returns first in this case
LWG 1338	C++98	the resolution of LWG issue 1205 was incorrectly applied, making first to be returned if no occurence is found	returns last in this case
LWG 2150	C++98	the condition of "sequence occurence" was incorrect	corrected