# uninitialized_copy_n

Categories: allocators, algorithms | Component type: function

### Prototype

    template <class InputIterator, class Size, class ForwardIterator>
    ForwardIterator uninitialized_copy_n(InputIterator first, Size count,
                                         ForwardIterator result);

### 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 `[result, result + n)` points to uninitialized memory, then `uninitialized_copy_n` creates a copy of `[first, first + n)` in that range. That is, for each iterator `i` in the input range, `uninitialized_copy_n` creates a copy of `*i` in the location pointed to by the corresponding iterator in the output range by calling `construct(&*(result + (i - first)), *i)`.

### Definition

Defined in the standard header memory, and in the nonstandard backward-compatibility header algo.h. This function is an SGI extension; it is not part of the C++ standard.

### Requirements on types

- `InputIterator` is a model of Input Iterator.
- `Size` is an integral type.
- `ForwardIterator` is a model of Forward Iterator.
- `ForwardIterator` is mutable.
- `ForwardIterator`'s value type has a constructor that takes a single argument whose type is `InputIterator`'s value type.

### Preconditions

- `n >= 0`
- `[first, first + n)` is a valid range.
- `[result, result + n)` is a valid range.
- Each iterator in `[result, result + 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()
    {
      int A1[] = {1, 2, 3, 4, 5, 6, 7};
      const int N = sizeof(A1) / sizeof(int);

      Int* A2 = (Int*) malloc(N * sizeof(Int));
      uninitialized_copy_n(A1, N, A2);
    }

### Notes

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

[2] `Uninitialized_copy_n` is almost, but not quite, redundant. If `first` is an input iterator, as opposed to a forward iterator, then the `uninitialized_copy_n` operation can't be expressed in terms of `uninitialized_copy`.

### See also

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

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