copy_n


Category: algorithms 
Component type: function 
Prototype
template <class InputIterator, class Size, class OutputIterator>
OutputIterator copy_n(InputIterator first, Size count,
OutputIterator result);
Description
Copy_n copies elements from the range [first, first + n) to the
range [result, result + n). That is, it performs the assignments
*result = *first, *(result + 1) = *(first + 1), and so on.
Generally, for every integer i from 0 up to (but not including)
n, copy_n performs the assignment *(result + i) = *(first + i).
Assignments are performed in forward order, i.e. in order of
increasing n. [1]
The return value is result + n.
Definition
Defined in the standard header algorithm, and in the nonstandard
backwardcompatibility header algo.h. This function is an SGI
extension; it is not part of the C++ standard.
Requirements on types

InputIterator is a model of Input Iterator.

OutputIterator is a model of Output Iterator.

Size is an integral type.

InputIterator's value type is convertible to a type in
OutputIterator's set of value types.
Preconditions

n >= 0.

[first, first + n) is a valid range.

result is not an iterator within the range [first, first + n).

[result, result + n) is a valid range.
Complexity
Linear. Exactly n assignments are performed.
Example
vector<int> V(5);
iota(V.begin(), V.end(), 1);
list<int> L(V.size());
copy_n(V.begin(), V.size(), L.begin());
assert(equal(V.begin(), V.end(), L.begin()));
Notes
[1]
Copy_n is almost, but not quite, redundant. If first is an
input iterator, as opposed to a forward iterator, then the
copy_n operation can't be expressed in terms of copy.
See also
copy, copy_backward