# C++ Algorithm Library - includes() Function

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## 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 binary function for comparison.

## Declaration

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

### C++98

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

## 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.

• comp − A binary function which accepts two arguments and returns bool.

## 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;

bool compare(char a, char b) {
return (tolower(a) == tolower(b));
}

int main(void) {
vector<char> v1 = {'a', 'b', 'c', 'd', 'e'};
vector<char> v2 = {'C', 'D', 'E'};
bool result;

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

if (result == true)
cout << "Vector v2 is 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
```
algorithm.htm