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Categories: allocators, algorithms Component type: function


template <class ForwardIterator, class Size, class T>
ForwardIterator uninitialized_fill_n(ForwardIterator first, Size n,
                                     const T& x);


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).


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

Requirements on types

  • ForwardIterator is a model of ForwardIterator.
  • 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.


  • 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.


Linear. Exactly n constructor calls.


class Int {
  Int(int x) : val(x) {}
  int get() { return val; }
  int val;

int main()
  const int N = 137;
  Int val(46);
  Int* A = (Int*) malloc(N * sizeof(Int));
  uninitialized_fill_n(A, N, val);


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

See also

Allocators, construct, destroy, uninitialized_copy, uninitialized_fill, raw_storage_iterator

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