fill_n

Article
08/22/2013

Assigns a new value to a specified number of elements in a range beginning with a particular element.

template<class OutputIterator, class Size, class Type> 
   OutputIterator fill_n( 
      OutputIterator First,  
      Size Count,  
      const Type& Val 
   );

Parameters

First
An output iterator addressing the position of the first element in the range to be assigned the value Val.
Count
A signed or unsigned integer type specifying the number of elements to be assigned the value.
Val
The value to be assigned to elements in the range [First, First + Count).

Return Value

An iterator to the element that follows the last element filled if Count > zero, otherwise the first element.

Remarks

The destination range must be valid; all pointers must be dereferenceable, and the last position is reachable from the first by incrementation. The complexity is linear with the size of the range.

fill_n has two related forms:

For information on how these functions behave, see Checked Iterators.

Example

// alg_fill_n.cpp
// compile using /EHsc
#include <vector>
#include <algorithm>
#include <iostream>

int main() 
{
    using namespace std;
    vector <int> v;

    for ( auto i = 0 ; i < 9 ; ++i )
        v.push_back( 0 );

    cout << "  vector v = ( " ;
    for ( const auto &w : v )
        cout << w << " ";
    cout << ")" << endl;

    // Fill the first 3 positions with a value of 1, saving position.
    auto pos = fill_n( v.begin(), 3, 1 );

    cout << "modified v = ( " ;
    for ( const auto &w : v )
        cout << w << " ";
    cout << ")" << endl;

    // Fill the next 3 positions with a value of 2, using last position.
    fill_n( pos, 3, 2 );

    cout << "modified v = ( " ;
    for ( const auto &w : v )
        cout << w << " ";
    cout << ")" << endl;

    // Fill the last 3 positions with a value of 3, using relative math.
    fill_n( v.end()-3, 3, 3 );

    cout << "modified v = ( " ;
    for ( const auto &w : v )
        cout << w << " ";
    cout << ")" << endl;
}

Output

  vector v = ( 0 0 0 0 0 0 0 0 0 )
modified v = ( 1 1 1 0 0 0 0 0 0 )
modified v = ( 1 1 1 2 2 2 0 0 0 )
modified v = ( 1 1 1 2 2 2 3 3 3 )

Requirements

Header: <algorithm>

Namespace: std