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 algo.h. The implementation is in algobase.h.

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.