std::search

Defined in header `<algorithm>`
	(1)
template< class ForwardIt1, class ForwardIt2 > ForwardIt1 search( ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last );		(until C++20)
template< class ForwardIt1, class ForwardIt2 > constexpr ForwardIt1 search( ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last );		(since C++20)
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)
	(3)
template< class ForwardIt1, class ForwardIt2, class BinaryPredicate > ForwardIt1 search( ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last, BinaryPredicate p );		(until C++20)
template< class ForwardIt1, class ForwardIt2, class BinaryPredicate > constexpr ForwardIt1 search( ForwardIt1 first, ForwardIt1 last, ForwardIt2 s_first, ForwardIt2 s_last, BinaryPredicate p );		(since C++20)
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)
	(5)
template< class ForwardIt, class Searcher > ForwardIt search( ForwardIt first, ForwardIt last, const Searcher& searcher );		(since C++17) (until C++20)
template< class ForwardIt, class Searcher > constexpr ForwardIt search( ForwardIt first, ForwardIt last, const Searcher& searcher );		(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 do not participate in overload resolution unless

`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. Searcher need not be CopyConstructible.

The standard library provides the following searchers:

default_searcher (C++17)	standard C++ library search algorithm implementation (class template)
boyer_moore_searcher (C++17)	Boyer-Moore search algorithm implementation (class template)
boyer_moore_horspool_searcher (C++17)	Boyer-Moore-Horspool search algorithm implementation (class template)

(since C++17)

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);` 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.

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.

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.

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 (3)
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; } }

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 (3)

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;
    }
}

Example

#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 `[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

find_end	finds the last sequence of elements in a certain range (function template)
includes	returns `true` if one sequence is a subsequence of another (function template)
equal	determines if two sets of elements are the same (function template)
findfind_iffind_if_not (C++11)	finds the first element satisfying specific criteria (function template)
lexicographical_compare	returns `true` if one range is lexicographically less than another (function template)
mismatch	finds the first position where two ranges differ (function template)
search_n	searches a range for a number of consecutive copies of an element (function template)
default_searcher (C++17)	standard C++ library search algorithm implementation (class template)
boyer_moore_searcher (C++17)	Boyer-Moore search algorithm implementation (class template)
boyer_moore_horspool_searcher (C++17)	Boyer-Moore-Horspool search algorithm implementation (class template)
ranges::search (C++20)	searches for a range of elements (niebloid)