Книга: Standard Template Library Programmer

uninitialized_fill_n

uninitialized_fill_n

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.

• 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.

• 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 {
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);
}

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

Allocators, construct, destroy, uninitialized_copy, uninitialized_fill, raw_storage_iterator

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