equal


function template
<algorithm>
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 );

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:
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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

true if all the elements in the range [first1,last1) compare equal to those of the range starting at first2, and false otherwise.

Example

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// 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

At most, performs as many comparisons or applications of pred as the number of elements in the range [first1,last1).

See also

mismatch Return first position where two ranges differ (function template)
find_first_of Find element from set in range (function template)
find_end Find last subsequence in range (function template)
search Find subsequence in range (function template)