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# std::reverse

From cppreference.com
< cpp‎ | algorithm

Defined in header `<algorithm>` |  |
template< class BidirIt > void reverse( BidirIt first, BidirIt last ); |  |

Reverses the order of the elements in the range `[first, last)`

Behaves as if applying std::iter_swap to every pair of iterators `first+i, (last-i) - 1` for each non-negative `i < (last-first)/2`

### [edit] Parameters

first, last | - | the range of elements to reverse
Type requirements
- `BidirIt` must meet the requirements of `BidirectionalIterator`.
- The type of dereferenced `BidirIt` must meet the requirements of `Swappable`.

### [edit] Return value

(none)

### [edit] Possible implementation

    template<class BidirIt>
    void reverse(BidirIt first, BidirIt last)
    {
        while ((first != last) && (first != --last)) {
            std::iter_swap(first++, last);
        }
    }

### [edit] Example

Run this code

    #include <vector>
    #include <iostream>
    #include <algorithm>

    int main()
    {
        std::vector<int> v({1,2,3});
        std::reverse(std::begin(v), std::end(v));
        std::cout << v[0] << v[1] << v[2] << '\n';

        int a[] = {4, 5, 6, 7};
        std::reverse(&a[0], &a[4]);
        std::cout << a[0] << a[1] << a[2] << a[3] << '\n';
    }

Output:

    321
    7654

### [edit] Complexity

linear in the distance between `first` and `last`

### [edit] See also

reverse_copy | creates a copy of a range that is reversed (function template) [edit]

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