"Insert before" for std::list

Question

Lets say I have a linked list which contains the following:

1, 2, 4, 5, 6, 2, 3, 2

now lets say I wish to convert this to:

1, 10, 2, 4, 5, 6, 10, 2, 3, 10, 2

i.e. insert 10 before all 2's.

How should I do this?

Answer 1

Off the top of my head

for (std::list<int>::iterator i = l.begin(); i != l.end(); ++i)
  if (*i == 2)
     l.insert(i, 10);

Simple enough. You don't need to worry about iterator invalidation because insert on a std::list does not invalidate any iterators. It's one of the advantages of using std::list.

Answer 2

Maybe something like this:

auto it = l.begin();
while ((it = std::find(it, l.end(), 2)) != l.end())
{
    it = l.insert(it, 10);
    std::advance(it, 2);
}