# rotate_copy  Category: algorithms Component type: function

### Prototype

```template <class ForwardIterator, class OutputIterator>
OutputIterator rotate_copy(ForwardIterator first, ForwardIterator middle,
ForwardIterator last, OutputIterator result);
```

### Description

Rotate_copy copies elements from the range [first, last) to the range [result, result + (last - first)) such that *middle is copied to *result, *(middle + 1) is copied to *(result + 1), and so on. Formally, for every integer n such that 0 <= n < last - first, rotate_copy performs the assignment *(result + (n + (last - middle)) % (last - first)) = *(first + n). Rotate_copy is similar to copy followed by rotate, but is more efficient. The return value is result + (last - first).

### Definition

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

### Requirements on types

• ForwardIterator is a model of Forward Iterator.
• OutputIterator is a model of Output Iterator.
• ForwardIterator's value type is convertible to a type in OutputIterator's set of value types.

### Preconditions

• [first, middle) is a valid range.
• [middle, last) is a valid range. 
• There is enough space to hold all of the elements being copied. More formally, the requirement is that [result, result + (last - first)) is a valid range.
• The ranges [first, last) and [result, result + (last - first)) do not overlap.

### Complexity

Linear. Rotate_copy performs exactly last - first assignments.

### Example

```const char alpha[] = "abcdefghijklmnopqrstuvwxyz";
rotate_copy(alpha, alpha + 13, alpha + 26, ostream_iterator<char>(cout));
// The output is nopqrstuvwxyzabcdefghijklm
```

### Notes

 It follows from these two requirements that [first, last) is a valid range.