 

Category: algorithms   Component type: function 
Prototype
template <class BidirectionalIterator1, class BidirectionalIterator2>
BidirectionalIterator2 copy_backward(BidirectionalIterator1 first,
BidirectionalIterator1 last,
BidirectionalIterator2 result);
Description
Copy_backward
copies elements from the range [first, last)
to the range [result  (last  first), result)
[1]. That is, it performs the assignments *(result  1) = *(last  1)
, *(result  2) = *(last  2)
, and so on. Generally, for every integer n
from 0
to last  first
, copy_backward
performs the assignment *(result  n  1) = *(last  n  1)
. Assignments are performed from the end of the input sequence to the beginning, i.e. in order of increasing n
. [2]
The return value is result  (last  first)
Definition
Defined in the standard header algorithm, and in the nonstandard backwardcompatibility header algo.h.
Requirements on types

BidirectionalIterator1 and BidirectionalIterator2 are models of BidirectionalIterator.

BidirectionalIterator1's value type is convertible to BidirectionalIterator2's value type.
Preconditions

[first, last)
is a valid range.

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

There is enough space to hold all of the elements being copied. More formally, the requirement is that
[result  (last  first), result)
is a valid range.
Complexity
Linear. Exactly last  first
assignments are performed.
Example
Vector<int> V(15);
iota(V.begin(), V.end(), 1);
copy_backward(V.begin(), V.begin() + 10, V.begin() + 15);
Notes
[1] Result
is an iterator that points to the end of the output range. This is highly unusual: in all other STL algorithms that denote an output range by a single iterator, that iterator points to the beginning of the range.
[2] The order of assignments matters in the case where the input and output ranges overlap: copy_backward
may not be used if result
is in the range [first, last)
. That is, it may not be used if the end of the output range overlaps with the input range, but it may be used if the beginning of the output range overlaps with the input range; copy
has opposite restrictions. If the two ranges are completely nonoverlapping, of course, then either algorithm may be used.
See also
copy
, copy_n