uninitialized_fill_n



Categories: allocators algorithms	Component type: function

Prototype

template <class ForwardIterator
class Size
class T>
ForwardIterator uninitialized_fill_n(ForwardIterator first
Size n

                                     const T& x);

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 [first first + n) points to uninitialized memory then uninitialized_fill_n creates copies of x in that range. That is for each iterator i in the range [first first + n) uninitialized_fill_n creates a copy of x in the location pointed to i by calling construct(&*i x).

Definition

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

Requirements on types

ForwardIterator is a model of Forward Iterator.
ForwardIterator is mutable.
Size is an integral type that is convertible to ForwardIterator's distance type.
ForwardIterator's value type has a constructor that takes a single argument of type T.

Preconditions

n is nonnegative.
[first first + n) is a valid range.
Each iterator in [first first + 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()
{
  const int N = 137;

  Int val(46);
  Int* A = (Int*) malloc(N * sizeof(Int));
  uninitialized_fill_n(A
N
val);
}

Notes

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