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fill_n() function in C++ STL with examples

Last Updated : 11 Oct, 2019
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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. Syntax:
void fill_n(iterator begin, int n, type value);
Parameters:
  • 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: CPP14
// 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;
}
Output:
7 7 7 7 0 0 0 0
 7 7 7 4 4 4 0 0
Reference: http://www.cplusplus.com/reference/algorithm/fill_n/

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