NAME¶

std::search - std::search

Synopsis¶

Defined in header <algorithm>
template< class ForwardIt1, class
ForwardIt2 >

ForwardIt1 search( ForwardIt1 first, (until C++20)
ForwardIt1 last,

ForwardIt2 s_first, ForwardIt2 s_last );
template< class ForwardIt1, class
ForwardIt2 >

constexpr ForwardIt1 search( ForwardIt1 (since C++20)
first, ForwardIt1 last,

ForwardIt2 s_first, ForwardIt2 s_last );
template< class ExecutionPolicy, class
ForwardIt1, class ForwardIt2 >

ForwardIt1 search( ExecutionPolicy&& (2) (since C++17)
policy,
ForwardIt1 first, ForwardIt1 last,

ForwardIt2 s_first, ForwardIt2 s_last );
template< class ForwardIt1, class
ForwardIt2, class BinaryPredicate >

ForwardIt1 search( ForwardIt1 first, (until C++20)
ForwardIt1 last,
ForwardIt2 s_first, ForwardIt2 s_last,

BinaryPredicate p );
template< class ForwardIt1, class (1)
ForwardIt2, class BinaryPredicate >

constexpr ForwardIt1 search( ForwardIt1 (since C++20)
first, ForwardIt1 last,
ForwardIt2 s_first, ForwardIt2 s_last,

BinaryPredicate p );
template< class ExecutionPolicy,

class ForwardIt1, class ForwardIt2,
class BinaryPredicate > (3)
ForwardIt1 search( ExecutionPolicy&& (4) (since C++17)
policy,
ForwardIt1 first, ForwardIt1 last,
ForwardIt2 s_first, ForwardIt2 s_last,

BinaryPredicate p );
template< class ForwardIt, class
Searcher > (since
C++17)
ForwardIt search( ForwardIt first, (until
ForwardIt last, C++20)

const Searcher& searcher ); (5)
template< class ForwardIt, class
Searcher >
(since
constexpr ForwardIt search( ForwardIt C++20)
first, ForwardIt last,

const Searcher& searcher );

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>>
(until C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>
(since 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;. Searcher need
not be CopyConstructible.

The standard library provides the following searchers:

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

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
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);

p - 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.
-
Searcher must meet the requirements of 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 no such occurrence is found, last is returned.
If [s_first, s_last) is empty, first is returned.
(since C++11)
5) Returns the result of searcher.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) At most S*N comparisons where S = std::distance(s_first, s_last) and N =
std::distance(first, last).
5) Depends on the 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¶

First version¶

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

Second version¶

template<class ForwardIt1, class ForwardIt2, class BinaryPredicate>
constexpr ForwardIt1 search(ForwardIt1 first, ForwardIt1 last,
ForwardIt2 s_first, ForwardIt2 s_last,
BinaryPredicate p)
{
while (1) {
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 <string_view>
#include <functional>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <vector>
#include <string>

template <typename Container>
bool contains(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 << contains(str, "learning") << '\n' // true
<< contains(str, "lemming") << '\n'; // false

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

// The C++17 overload demo:
constexpr std::string_view haystack =
"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed "
"do eiusmod tempor incididunt ut labore et dolore magna aliqua";
const std::string needle {"pisci"};

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

Output:¶

true
false
true
false
The string 'pisci' found at offset 43

See also¶

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