# uninitialized_fill_n

Categories: allocators, algorithms | Component type: function

### Prototype

    template <class ForwardIterator, class Size, class T>
    ForwardIterator uninitialized_fill_n(ForwardIterator first, Size n,
                                         const T& x);

### Description

In C++, the operator `new` allocates memory for an object and then creates an object at that location by calling a constructor. Occasionally, however, it is useful to separate those two operations. [1] If each iterator in the range `[first, first + n)` points to uninitialized memory, then `uninitialized_fill_n` creates copies of `x` in that range. That is, for each iterator `i` in the range `[first, first + n)`, `uninitialized_fill_n` creates a copy of `x` in the location pointed to `i` by calling `construct(&*i, x)`.

### Definition

Defined in the standard header memory, and in the nonstandard backward-compatibility header algo.h.

### Requirements on types

- `ForwardIterator` is a model of Forward Iterator.
- `ForwardIterator` is mutable.
- `Size` is an integral type that is convertible to `ForwardIterator`'s distance type.
- `ForwardIterator`'s value type has a constructor that takes a single argument of type `T`.

### Preconditions

- `n` is nonnegative.
- `[first, first + n)` is a valid range.
- Each iterator in `[first, first + n)` points to a region of uninitialized memory that is large enough to store a value of `ForwardIterator`'s value type.

### Complexity

Linear. Exactly `n` constructor calls.

### Example

    class Int {
    public:
      Int(int x) : val(x) {}
      int get() { return val; }
    private:
      int val;
    };

    int main()
    {
      const int N = 137;

      Int val(46);
      Int* A = (Int*) malloc(N * sizeof(Int));
      uninitialized_fill_n(A, N, val);
    }

### Notes

[1] In particular, this sort of low-level memory management is used in the implementation of some container classes.

### See also

Allocators, `construct`, `destroy`, `uninitialized_copy`, `uninitialized_fill`, `raw_storage_iterator`

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