# C++ Algorithm Library - equal() Function

## Description

The C++ function std::algorithm::equal() tests whether two sets of element are equal or not. Size of the both set need not to be equal. It uses binary predicate for comparison.

## Declaration

Following is the declaration for std::algorithm::equal() function form std::algorithm header.

### C++98

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

## Parameters

• first1 − Input iterator to the initial position of the first sequence.

• last1 − Input iterator to the final position of the first sequence.

• first2 − Input iterator to the initial position of the second sequence.

• pred − A binary predicate which accepts two arguments and returns a bool.

## Return value

Returns true if all the element in the range of first1 to last1 are equal to those of the range starting at first2 otherwise it returns false.

## Exceptions

Throws exception if either element comparison (or predicate) or an operation on an iterator throws exception.

Please note that invalid parameters cause undefined behavior.

## Time complexity

Linear in the distance between first to last.

## Example

The following example shows the usage of std::algorithm::equal() function.

```#include <iostream>
#include <vector>
#include <algorithm>
#include <string>

using namespace std;

/* Binary predicate which always returns true */
bool binary_pred(string s1, string s2) {
return true;
}

int main(void) {
vector<string> v1 = {"one", "two", "three"};
vector<string> v2 = {"ONE", "THREE", "THREE"};
bool result;

result = equal(v1.begin(), v1.end(), v2.begin(), binary_pred);

if (result == true)
cout << "Vector range is equal." << endl;

return 0;
}
```

Let us compile and run the above program, this will produce the following result −

```Vector range is equal.
```
algorithm.htm