adjacent_find()

Library:  Algorithms

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An algorithm that finds the first adjacent pair of equivalent elements in a sequence

#include <algorithm>

namespace std {
  template <class ForwardIterator>
    ForwardIterator
    adjacent_find(ForwardIterator start, 
                  ForwardIterator finish);

  template <class ForwardIterator, class BinaryPredicate>
    ForwardIterator
    adjacent_find(ForwardIterator start, 
                  ForwardIterator finish,
                  BinaryPredicate binary_pred);
}

There are two variations of the adjacent_find() algorithm. The first finds equal adjacent elements in the sequence defined by iterators start and finish and returns an iterator i pointing to the first of the equal elements. The second variation lets you specify a binary function object to test for a condition. The algorithm returns an iterator i pointing to the first of the pair of elements that meet the conditions of the binary function. In other words, adjacent_find() returns the first iterator i where both i and i + 1 are in the range [start, finish) that meets one of the following conditions:

*i == *(i + 1)

or

binary_pred(*i,*(i + 1)) == true

If adjacent_find() does not find a match, it returns finish.

adjacent_find() performs exactly find(start,finish,value) - start applications of the corresponding predicate.

//
//  find.cpp
//

#include <vector>      // for vector
#include <algorithm>   // for adjacent_find, find
#include <functional>  // for bind1st, equal_to
#include <iostream>    // for cout, endl



int main ()
{
    // Typedef for convenience.
    typedef std::vector<int, std::allocator<int> > Vector;

    const Vector::value_type arr[] = { 0, 1, 2, 2, 3, 
                                       4, 2, 2, 6, 7 };

    // Set up a vector.
    const Vector v1 (arr, arr + sizeof arr / sizeof *arr);

    // Try find.
    Vector::const_iterator it = std::find (v1.begin (), 
                                           v1.end (), 3);

    std::cout << *it << ' ';

    // Try find_if.
    it = std::find_if (v1.begin (), v1.end (),
             std::bind1st (std::equal_to<Vector::value_type>(), 
             3));

    std::cout << *it << ' ';

    // Try both adjacent_find variants.
    it = std::adjacent_find (v1.begin (), v1.end ());

    std::cout << *it << ' ';

    it = std::adjacent_find (v1.begin (), v1.end (),
                          std::equal_to<Vector::value_type>());

    std::cout << *it << std::endl;

    return 0;
}


Program Output:

3 3 2 2

find()

ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 25.1.5