std::search_n
Defined in header <algorithm> | ||
---|---|---|
(1) | ||
template< class ForwardIt, class Size, class T > ForwardIt search_n( ForwardIt first, ForwardIt last, Size count, const T& value ); | (until C++20) | |
template< class ForwardIt, class Size, class T > constexpr ForwardIt search_n( ForwardIt first, ForwardIt last, Size count, const T& value ); | (since C++20) | |
template< class ExecutionPolicy, class ForwardIt, class Size, class T > ForwardIt search_n( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, Size count, const T& value ); | (2) | (since C++17) |
(3) | ||
template< class ForwardIt, class Size, class T, class BinaryPredicate > ForwardIt search_n( ForwardIt first, ForwardIt last, Size count, const T& value, BinaryPredicate p ); | (until C++20) | |
template< class ForwardIt, class Size, class T, class BinaryPredicate > constexpr ForwardIt search_n( ForwardIt first, ForwardIt last, Size count, const T& value, BinaryPredicate p ); | (since C++20) | |
template< class ExecutionPolicy, class ForwardIt, class Size, class T, class BinaryPredicate > ForwardIt search_n( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, Size count, const T& value, BinaryPredicate p ); | (4) | (since C++17) |
Searches the range [first, last)
for the first sequence of count identical elements, each equal to the given value value.
operator==
.p
.policy
. These overloads do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>
is trueParameters
first, last | - | the range of elements to examine |
count | - | the length of the sequence to search for |
value | - | the value of the elements to search for |
policy | - | the execution policy to use. See execution policy for details. |
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:
While the signature does not need to have |
Type requirements | ||
-ForwardIt must meet the requirements of LegacyForwardIterator. |
Return value
Iterator to the beginning of the found sequence in the range [first, last)
. If no such sequence is found, last
is returned.
If count
is zero or negative, first
is returned.
Complexity
At most last - first
applications of the predicate.
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 otherExecutionPolicy
, the behavior is implementation-defined. - If the algorithm fails to allocate memory,
std::bad_alloc
is thrown.
Possible implementation
First version |
---|
template<class ForwardIt, class Size, class T> ForwardIt search_n(ForwardIt first, ForwardIt last, Size count, const T& value) { if (count <= 0) { return first; } for(; first != last; ++first) { if (!(*first == value)) { continue; } ForwardIt candidate = first; Size cur_count = 0; while (true) { ++cur_count; if (cur_count >= count) { // success return candidate; } ++first; if (first == last) { // exhausted the list return last; } if (!(*first == value)) { // too few in a row break; } } } return last; } |
Second version |
template<class ForwardIt, class Size, class T, class BinaryPredicate> ForwardIt search_n(ForwardIt first, ForwardIt last, Size count, const T& value, BinaryPredicate p) { if (count <= 0) { return first; } for(; first != last; ++first) { if (!p(*first, value)) { continue; } ForwardIt candidate = first; Size cur_count = 0; while (true) { ++cur_count; if (cur_count >= count) { // success return candidate; } ++first; if (first == last) { // exhausted the list return last; } if (!p(*first, value)) { // too few in a row break; } } } return last; } |
Example
#include <iostream> #include <algorithm> #include <iterator> template <class Container, class Size, class T> bool consecutive_values(const Container& c, Size count, const T& v) { return std::search_n(std::begin(c),std::end(c),count,v) != std::end(c); } int main() { const char sequence[] = "1001010100010101001010101"; std::cout << std::boolalpha; std::cout << "Has 4 consecutive zeros: " << consecutive_values(sequence,4,'0') << '\n'; std::cout << "Has 3 consecutive zeros: " << consecutive_values(sequence,3,'0') << '\n'; }
Output:
Has 4 consecutive zeros: false Has 3 consecutive zeros: true
See also
finds the last sequence of elements in a certain range (function template) |
|
(C++11) | finds the first element satisfying specific criteria (function template) |
searches for a range of elements (function template) |
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