Reversing Elements in std::forward_list

The reverse() member function in std::forward_list reverses the order of the elements in the list.

1#include <forward_list>
2#include <iostream>
3
4int main() {
5  std::forward_list<int> list{1, 2, 3, 4, 5};
6
7  list.reverse();  
8
9  for (int i : list) {
10    std::cout << i << ' ';
11  }
12}

15 4 3 2 1

After calling reverse(), the order of the elements is reversed.

Note that reversing a forward_list is a linear time operation, as it needs to traverse the entire list to reverse the links between the nodes.

Also, since forward_list is a singly-linked list, there's no rbegin() or rend() for reverse iteration. If you need to frequently access the elements in reverse order, you might consider using a different container like list (doubly-linked list) or deque (double-ended queue), which provide bidirectional iterators.

1#include <forward_list>
2#include <iostream>
3
4int main() {
5  std::forward_list<int> list{1, 2, 3, 4, 5};
6
7  for (
8    auto it = list.rbegin();
9    it != list.rend();
10    ++it
11  ) {
12    std::cout << *it << ' ';
13  }
14}

1error: 'rbegin': is not a member of 'std::forward_list'
2error: 'rend': is not a member of 'std::forward_list'

However, if you only need to reverse the elements once, reverse() is a convenient and efficient method.