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# std::fill_n

From cppreference.com
< cpp‎ | algorithm

Defined in header `<algorithm>` |  |

template< class OutputIt, class Size, class T > void fill_n( OutputIt first, Size count, const T& value ); |  | (until C++11)
template< class OutputIt, class Size, class T > OutputIt fill_n( OutputIt first, Size count, const T& value ); |  | (since C++11)

Assigns the given value `value` to the first `count` elements in the range beginning at `first` if `count > 0`. Does nothing otherwise.

### [edit] Parameters

first | - | the beginning of the range of elements to modify
count | - | number of elements to modify
value | - | the value to be assigned
Type requirements
- `OutputIt` must meet the requirements of `OutputIterator`.

### [edit] Return value

(none) | (until C++11)
Iterator one past the last element assigned if `count > 0`, `first` otherwise. | (since C++11)

### [edit] Complexity

Exactly `count` assignments, for `count > 0`.

### [edit] Possible implementation

    template<class OutputIt, class Size, class T>
    OutputIt fill_n(OutputIt first, Size count, const T& value)
    {
        for (Size i = 0; i < count; i++) {
            *first++ = value;
        }
        return first;
    }

### [edit] Example

The following code uses `fill_n()` to assign -1 to the first half of a vector of integers:

Run this code

    #include <algorithm>
    #include <vector>
    #include <iostream>
    #include <iterator>

    int main()
    {
        std::vector<int> v1{0, 1, 2, 3, 4, 5, 6, 7, 8, 9};

        std::fill_n(v1.begin(), 5, -1);

        std::copy(begin(v1), end(v1), std::ostream_iterator<int>(std::cout, " "));
        std::cout << "\n";
    }

Output:

    -1 -1 -1 -1 -1 5 6 7 8 9

### [edit] See also

fill | assigns a range of elements a certain value (function template) [edit]

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