Книга: Standard Template Library Programmer

raw_storage_iterator

raw_storage_iterator<ForwardIterator, T>

Categories: allocators, iterators, adaptors

Component type: type

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).

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>());
}

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

Output Iterator

• ForwardIterator is a model of Forward Iterator

• ForwardIterator's value type has a constructor that takes a single argument of type T.

None.

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

[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.

Allocators, construct, destroy, uninitialized_copy uninitialized_fill, uninitialized_fill_n

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