# C++ Algorithm Library - includes() Function

## Description

The C++ function std::algorithm::includes() test whether first set is subset of another or not. This member function expects elements in sorted order. It use operator< for comparison.

## Declaration

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

### C++98

```template <class InputIterator1, class InputIterator2>
bool includes(InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2);
```

## 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.

• last2 − Input iterator to the final position of the second sequence.

## Return value

Returns true if first set is subset of another otherwise returns false.

## Exceptions

Throws exception if element comparison or an operation on an iterator throws exception.

Please note that invalid parameters cause undefined behavior.

Linear.

## Example

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

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

using namespace std;

int main(void) {
vector<int> v1 = {1, 2, 3, 4, 5};
vector<int> v2 = {3, 4, 5};
bool result;

result = includes(v1.begin(), v1.end(), v2.begin(), v2.end());

if (result == true)
cout << "Vector v2 is subset of v1" << endl;

v2 = {10};

result = includes(v1.begin(), v1.end(), v2.begin(), v2.end());

if (result == false)
cout << "Vector v2 is not subset of v1" << endl;

return 0;
}
```

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

```Vector v2 is subset of v1
Vector v2 is not subset of v1
```
algorithm.htm