std::adjacent_find

 

C++

Language

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

 

Algorithm library

Functions
Non-modifying sequence operations
all_of any_of none_of (C++11) (C++11) (C++11) for_each count count_if mismatch equal	find find_if find_if_not (C++11) find_end find_first_of adjacent_find search search_n
Modifying sequence operations
copy copy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) fill fill_n transform generate generate_n remove remove_if remove_copy remove_copy_if	replace replace_if replace_copy replace_copy_if swap swap_ranges iter_swap reverse reverse_copy rotate rotate_copy random_shuffle shuffle   (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 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 > ForwardIt adjacent_find( ForwardIt first, ForwardIt last );	(1)
template< class ForwardIt, BinaryPredicate p > ForwardIt adjacent_find( ForwardIt first, ForwardIt last, BinaryPredicate p );	(2)

Searches the range [first, last) for two consecutive identical elements. 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
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 types  Type1 and  Type2 must be such that an object of type ForwardIt can be dereferenced and then implicitly converted to both of them. ​
Type requirements
- ForwardIt must meet the requirements of ForwardIterator.

Return value

an iterator to the first of the identical elements. If no such elements are found, last is returned

Complexity

Exactly the smaller of (result - first) + 1 and (last - first) - 1 applications of the predicate where result is the return value.

Possible implementation

First version
template<class ForwardIt> ForwardIt adjacent_find(ForwardIt first, ForwardIt last) { if (first == last) { return last; } ForwardIt next = first; ++next; for (next != last; ++next, ++first) { if (*first == *next) { return first; } } return last; }
Second version
template<class ForwardIt, BinaryPredicate p> ForwardIt adjacent_find(ForwardIt first, ForwardIt last, BinaryPredicate p) { if (first == last) { return last; } ForwardIt next = first; ++next; for (next != last; ++next, ++first) { if (p(*first, *next)) { return first; } } return last; }

Example

The following code finds a pair of equivalent integers in an array of intergers.

#include <algorithm>
#include <iostream>
 
int main()
{
    std::vector<int> v1{0, 1, 2, 3, 40, 40, 5};
 
    std::vector<int>::iterator result;
    result = std::adjacent_find(v1.begin(), v1.end());
 
    if (result == v1.end()) {
        std::cout << "no matching adjacent elements";
    } else {
        std::cout << "match at: " << std::distance(v1.begin(), result);
    }
}

Output:

match at: 4

See also

unique	removes consecutive duplicate elements in a range (function template)