Книга: Standard Template Library Programmer

uninitialized_copy_n

uninitialized_copy_n

Categories: allocators, algorithms

Component type: function

template <class InputIterator, class Size, class ForwardIterator>
ForwardIterator uninitialized_copy_n(InputIterator first, Size count, ForwardIterator result);

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).

Defined in the standard header memory, and in the nonstandard backward-compatibility header algo.h. This function is an SGI extension; it is not part of the C++ standard.

• 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.

• 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.

Linear. Exactly n constructor calls.

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);
}

[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.

Allocators, construct, destroy, uninitialized_copy, uninitialized_fill, uninitialized_fill_n, raw_storage_iterator

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