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.