# raw_storage_iterator<ForwardIterator, T>

Categories: allocators, iterators, adaptors | Component type: type

### 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 `i` is an iterator that points to a region of uninitialized memory, then you can use `construct` to create an object in the location pointed to by `i`. `Raw_storage_iterator` is an adaptor that makes this procedure more convenient. If `r` is a `raw_storage_iterator`, then it has some underlying iterator `i`. The expression `*r = x` is equivalent to `construct(&*i, x)`.

### 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));
      transform(A1, A1 + N,
                raw_storage_iterator<Int*, int>(A2),
                negate<int>());
    }

### Definition

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

### Template parameters

Parameter | Description | Default
--- | --- | ---
OutputIterator | The type of the `raw_storage_iterator`'s underlying iterator. |
`T` | The type that will be used as the argument to the constructor. |

### Model of

Output Iterator

### Type requirements

- `ForwardIterator` is a model of Forward Iterator
- `ForwardIterator`'s value type has a constructor that takes a single argument of type `T`.

### Public base classes

None.

### Members

Member | Where defined | Description
--- | --- | ---
`raw_storage_iterator(ForwardIterator x)` | `raw_storage_iterator` | See below.
`raw_storage_iterator(const raw_storage_iterator&)` | trivial iterator | The copy constructor
`raw_storage_iterator& operator=(const raw_storage_iterator&)` | trivial iterator | The assignment operator
`raw_storage_iterator& operator*()` | Output Iterator | Used to implement the output iterator expression `*i = x`. [2]
`raw_storage_iterator& operator=(const Sequence::value_type&)` | Output Iterator | Used to implement the output iterator expression `*i = x`. [2]
`raw_storage_iterator& operator++()` | Output Iterator | Preincrement.
`raw_storage_iterator& operator++(int)` | Output Iterator | Postincrement.
`output_iterator_tag iterator_category(const raw_storage_iterator&)` | iterator tags | Returns the iterator's category. This is a global function, not a member.

### New members

These members are not defined in the Output Iterator requirements, but are specific to `raw_storage_iterator`.

Function | Description
--- | ---
`raw_storage_iterator(ForwardIterator i)` | Creates a `raw_storage_iterator` whose underlying iterator is `i`.
`raw_storage_iterator& operator=(const T& val)` | Constructs an object of `ForwardIterator`'s value type at the location pointed to by the iterator, using `val` as the constructor's argument.

### Notes

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

[2] Note how assignment through a `raw_storage_iterator` is implemented. In general, unary `operator*` must be defined so that it returns a proxy object, where the proxy object defines `operator=` to perform the insert operation. In this case, for the sake of simplicity, the proxy object is the `raw_storage_iterator` itself. That is, `*i` returns `i`, and `*i = t` is equivalent to `i = t`. You should not, however, rely on this behavior. It is an implementation detail, and it is not guaranteed to remain the same in future versions.

### See also

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

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