fill_n() function in C++ STL with examples

The fill_n() function in C++ STL is used to fill some default values in a container. The fill_n() function is used to fill values upto first n positions from a starting position. It accepts an iterator begin and the number of positions n as arguments and fills the first n position starting from the position pointed by begin with the given value.


void fill_n(iterator begin, int n, type value);


  • begin: The function will start filling values from the position pointed by the iterator begin.
  • n: This parameter denotes the number of positions to be filled starting from the position pointed by first parameter begin.
  • value: This parameter denotes the value to be filled by the function in the container.

Return Value: This function does not returns any value.

Below program illustrate the fill_n() function in C++ STL:





// C++ program to demonstrate working of fil_n()
#include <bits/stdc++.h>
using namespace std;
int main()
    vector<int> vect(8);
    // calling fill to initialize first four values
    // to 7
    fill_n(vect.begin(), 4, 7);
    for (int i = 0; i < vect.size(); i++)
        cout << ' ' << vect[i];
    cout << '\n';
    // calling fill to initialize 3 elements from
    // "begin()+3" with value 4
    fill_n(vect.begin() + 3, 3, 4);
    for (int i = 0; i < vect.size(); i++)
        cout << ' ' << vect[i];
    cout << '\n';
    return 0;



7 7 7 7 0 0 0 0
 7 7 7 4 4 4 0 0


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