std::search_n

 

C++

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Technical Specifications

 

Algorithm library

Functions
Non-modifying sequence operations
all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each countcount_if mismatch equal	findfind_iffind_if_not (C++11) find_end find_first_of adjacent_find search search_n
Modifying sequence operations
copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) fill fill_n transform generate generate_n removeremove_if remove_copyremove_copy_if	replacereplace_if replace_copyreplace_copy_if swap swap_ranges iter_swap reverse reverse_copy rotate rotate_copy random_shuffleshuffle (until C++17)(C++11) unique unique_copy
Partitioning operations
is_partitioned (C++11) partition partition_copy (C++11)	stable_partition partition_point (C++11)
Sorting operations (on sorted ranges)
is_sorted (C++11) is_sorted_until (C++11) sort	partial_sort partial_sort_copy stable_sort nth_element
Binary search operations (on sorted ranges)
lower_bound upper_bound	binary_search equal_range
Set operations (on sorted ranges)
merge inplace_merge includes	set_difference set_intersection set_symmetric_difference set_union
Heap operations
is_heap (C++11) is_heap_until (C++11) make_heap	push_heap pop_heap sort_heap
Minimum/maximum operations
max max_element min min_element minmax (C++11) minmax_element (C++11)	lexicographical_compare is_permutation (C++11) next_permutation prev_permutation
Numeric operations
iota (C++11) accumulate inner_product	adjacent_difference partial_sum
C library
qsort	bsearch

 

Defined in header <algorithm>
template< class ForwardIt, class Size, class T > ForwardIt search_n( ForwardIt first, ForwardIt last, Size count, const T& value );	(1)
template< class ForwardIt, class Size, class T, class BinaryPredicate > ForwardIt search_n( ForwardIt first, ForwardIt last, Size count, const T& value,                      BinaryPredicate p );	(2)

Searches the range [first, last) for the first sequence of count identical elements, each equal to the given value value. The first version uses operator== to compare the elements, the second version uses the given binary predicate p.

Parameters

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
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); The signature does not need to have const &, but the function must not modify the objects passed to it. The type Type1 must be such that an object of type ForwardIt can be dereferenced and then implicitly converted to Type1. The type Type2 must be such that an object of type T can be implicitly converted to Type2. ​
Type requirements
- ForwardIt must meet the requirements of ForwardIterator.

Return value

Iterator to the beginning of the found sequence in the range [first, last). If no such sequence is found, last is returned.

Complexity

At most last - first applications of the predicate.

Possible implementation

First version
template<class ForwardIt, class Size, class T> ForwardIt search_n(ForwardIt first, ForwardIt last, Size count, const T& value) { 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) { 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

Run this code

#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

find_end	finds the last sequence of elements in a certain range (function template)
findfind_iffind_if_not (C++11)	finds the first element satisfying specific criteria (function template)
search	searches for a range of elements (function template)
std::experimental::parallel::search_n (parallelism TS)	parallelized version of std::search_n (function template)