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std::equal() in C++
  • Difficulty Level : Basic
  • Last Updated : 24 Jul, 2017

std::equal() helps to compares the elements within the range [first_1,last_1) with those within range beginning at first_2.
Syntax 1:

template 
  bool equal (InputIterator1 first1, InputIterator1 last1,
              InputIterator2 first2)
	
first_1, last_1 : Initial and final positions of the first
    sequence. All the elements are present within a range [first_1,last_1)
first2 : Initial position of the second sequence.

Returns : 
true, if all of the elements in both ranges match; otherwise false




// C++ program illustrating
// use of  bool equal (InputIterator1 first1, InputIterator1 last1,
// InputIterator2 first2)
      
  
#include <bits/stdc++.h>
  
int main()
{
    int v1[] = { 10, 20, 30, 40, 50 };
    std::vector<int> vector_1 (v1, v1 + sizeof(v1) / sizeof(int) );
  
    // Printing vector1
    std::cout << "Vector contains : ";
    for (unsigned int i = 0; i < vector_1.size(); i++)
        std::cout << " " << vector_1[i];
    std::cout << "\n";
  
    // using std::equal()
    // Comparison within default constructor
    if ( std::equal (vector_1.begin(), vector_1.end(), v1) )
        std::cout << "The contents of both sequences are equal.\n";
    else
        printf("The contents of both sequences differ.");
  
}

Output:

Vector contains :  10, 20, 30, 40, 50
The contents of both sequences are equal.

Syntax 2:

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

first_1, last_1 : Initial and final positions of the first
    sequence. All the elements are present within a range [first_1,last_1)
first2 : Initial position of the second sequence.
pred : Binary function that accepts two elements as argument 
      and returns a value convertible to boolean.

Returns : 
true, if all of the elements in both ranges match; otherwise false




// C++ program illustrating
// use of bool equal (InputIterator1 first1, InputIterator1 last1,
// InputIterator2 first2, BinaryPredicate pred);
  
#include <bits/stdc++.h>
  
bool pred(int i, int j)
{
    return (i != j);
}
  
int main()
{
    int v1[] = { 10, 20, 30, 40, 50 };
    std::vector<int> vector_1 (v1, v1 + sizeof(v1) / sizeof(int) );
  
    // Printing vector1
    std::cout << "Vector contains : ";
    for (unsigned int i = 0; i < vector_1.size(); i++)
        std::cout << " " << vector_1[i];
    std::cout << "\n";
  
    // using std::equal()
    // Comparison based on pred
    if ( std::equal (vector_1.begin(), vector_1.end(), v1, pred) )
        std::cout << "The contents of both sequences are equal.\n";
    else
        printf("The contents of both sequences differ.");
  
}

Output:

Vector contains :  10, 20, 30, 40, 50
The contents of both sequences differ.

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