# C++ Algorithm Library - is_partitioned() Function

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## Description

The C++ function std::algorithm::is_partitioned() tests whether range is partitioned or not. For empty ranges this function returns true.

## Declaration

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

### C++11

```template <class InputIterator, class UnaryPredicate>
bool is_partitioned (InputIterator first, InputIterator last, UnaryPredicate pred);
```

## Parameters

• first − Input iterator to the initial position.

• last − Input iterator to the final position.

• pred − A unary function which accepts an element and returns a bool.

## Return value

Returns true if range is partitioned otherwise it returns false.

## Exceptions

Throws exception if either the pred 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::is_partitioned() function.

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

using namespace std;

bool is_even(int n) {
return (n % 2 == 0);
}

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

result = is_partitioned(v.begin(), v.end(), is_even);

if (result == false)
cout << "Vector is not partitioned." << endl;

partition(v.begin(), v.end(), is_even);

result = is_partitioned(v.begin(), v.end(), is_even);

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

return 0;
}
```

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

```Vector is not partitioned.
Vector is paritioned.
```
algorithm.htm