C++ <algorithm> - fill_n() Function

The C++ algorithm::fill_n function is used to assign val to the first n elements of the sequence pointed by first.

Syntax

C++98
C++11

template <class OutputIterator, class Size, class T>
  void fill_n (OutputIterator first, 
               Size n, 
               const T& val);

template <class OutputIterator, class Size, class T>
  OutputIterator fill_n (OutputIterator first, 
                         Size n, 
                         const T& val);

Parameters

`first`	Specify initial position of the output iterator.
`n`	Specify number of elements to be filled.
`val`	Specify the value to be filled.

Return Value

Returns an iterator pointing to the element that follows the last element filled or None(in C++98).

Time Complexity

Linear i.e, Θ(n).

Example:

In the example below, the algorithm::fill_n function is used to fill the specified value in the given sequence.

#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
 
int main (){
  vector<int> vec(10);
  vector<int>::iterator it;

  cout<<"vec contains:";
  for(it = vec.begin(); it != vec.end(); ++it)
    cout<<" "<<*it;

  //fill first five element as 10
  fill_n(vec.begin(), 5, 10);

  cout<<"\nvec contains:";
  for(it = vec.begin(); it != vec.end(); ++it)
    cout<<" "<<*it;

  //fill two elements as 100 starting 
  //from third element
  fill_n(vec.begin()+2, 2, 100);

  cout<<"\nvec contains:";
  for(it = vec.begin(); it != vec.end(); ++it)
    cout<<" "<<*it;

  return 0;
}

The output of the above code will be:

vec contains: 0 0 0 0 0 0 0 0 0 0
vec contains: 10 10 10 10 10 0 0 0 0 0
vec contains: 10 10 100 100 10 0 0 0 0 0

❮ C++ <algorithm> Library