std::reverse

template <class BidirectionalIterator> void reverse (BidirectionalIterator first, BidirectionalIterator last);

Reverse range

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

The function calls iter_swap to swap the elements to their new locations.

The behavior of this function template is equivalent to:

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

Parameters

first, last: Bidirectional iterators to the initial and final positions of the sequence to be reversed. The range used is [first,last), which contains all the elements between first and last, including the element pointed by first but not the element pointed by last.
BidirectionalIterator shall point to a type for which swap is properly defined.

Return value

none

Example

// reverse algorithm example
#include <iostream> // std::cout
#include <algorithm> // std::reverse
#include <vector> // std::vector
int main () {
 std::vector<int> myvector;
 // set some values:
 for (int i=1; i<10; ++i) myvector.push_back(i); // 1 2 3 4 5 6 7 8 9
 std::reverse(myvector.begin(),myvector.end()); // 9 8 7 6 5 4 3 2 1
 // print out content:
 std::cout << "myvector contains:";
 for (std::vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)
 std::cout << ' ' << *it;
 std::cout << '\n';
 return 0;
}

Output:

myvector contains: 9 8 7 6 5 4 3 2 1

Complexity

Linear in half the distance between first and last: Swaps elements.

Data races

The objects in the range [first,last) are modified.

Exceptions

Throws if either an element swap or an operation on an iterator throws.
Note that invalid arguments cause undefined behavior.