template <class InputIterator1, class InputIterator2>
  bool equal ( InputIterator1 first1, InputIterator1 last1,
               InputIterator2 first2 );

template <class InputIterator1, class InputIterator2, class BinaryPredicate>
  bool equal ( InputIterator1 first1, InputIterator1 last1,
               InputIterator2 first2, BinaryPredicate pred );

<algorithm>

Test whether the elements in two ranges are equal

Compares the elements in the range [first1,last1) with those in the range beginning at first2, and returns true if the elements in both ranges are considered equal.

The elements are compared by either applying the == comparison operator to each pair of corresponding elements, or the template parameter comp (for the second version).

The behavior of this function template is equivalent to:

template <class InputIterator1, class InputIterator2>
  bool equal ( InputIterator1 first1, InputIterator1 last1, InputIterator2 first2 )
{
  while ( first1!=last1 )
  {
    if (*first1 != *first2)   // or: if (!pred(*first1,*first2)), for pred version
      return false;
    ++first1; ++first2;
  }
  return true;
}

Parameters

first1, last1

Forward iterators to the initial and final positions of the first sequence. The range used is [first1,last1), which contains all the elements between first1 and last1, including the element pointed by first1 but not the element pointed by last1.

first2

Forward iterator to the initial position of the second sequence. The comparison includes up to as many elements in this sequence as in the above sequence.

pred

Binary predicate taking two elements as argument (one of each of the two sequences), and returning the result of the comparison between them, with true (non-zero) meaning that they are to be considered equal, and false (zero) that they are not-equal. This can either be a pointer to a function or an object whose class overloads operator().

Return value

Example

// equal algorithm example
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

bool mypredicate (int i, int j) {
  return (i==j);
}

int main () {

  int myints[] = {20,40,60,80,100};          //   myints: 20 40 60 80 100
  vector<int>myvector (myints,myints+5);     // myvector: 20 40 60 80 100

  // using default comparison:
  if (equal (myvector.begin(), myvector.end(), myints))
    cout << "The contents of both sequences are equal." << endl;
  else
    cout << "The contents of both sequences differ." << endl;

  myvector[3]=81;                            // myvector: 20 40 60 81 100

  // using predicate comparison:
  if (equal (myvector.begin(), myvector.end(), myints, mypredicate))
    cout << "The contents of both sequences are equal." << endl;
  else
    cout << "The contents of both sequences differ." << endl;
  
  return 0;
}

Output:

The contents of both sequences are equal.
The contents of both sequence differ.

Complexity

See also