# C++ Algorithm Library - copy_n() Function

## Description

The C++ function std::algorithm::copy_n() copies first n numbers to a new location. If value of n is negative then function does nothing.

## Declaration

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

### C++11

```template <class InputIterator, class Size, class OutputIterator>
OutputIterator copy_n (InputIterator first, Size n, OutputIterator result);
```

## Parameters

• first − Input iterators to the initial positions of the searched sequence.

• n − Number of elements to copy.

• result − Output iterator to the initial position in the new sequence.

## Return value

Returns an iterator to the end of the destination range where elements have been copied.

## Exceptions

Throws an exception if either element assignment 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::copy_n() function.

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

using namespace std;

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

copy_n(v1.begin(), 3, v2.begin());

cout << "Vector v2 contains following elements" << endl;

for (auto it = v2.begin(); it != v2.end(); ++it)
cout << *it << endl;

return 0;
}
```

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

```Vector v2 contains following elements
1
2
3
```
algorithm.htm