I have a std::deque, and I want to insert an element at a specified index (I'm aware that std::list would be better at this). The deque::insert() function takes an iterator to specify the location to insert. Given an index, how can I get an iterator pointing to that location, so that I can pass that iterator to insert()?

For example:

void insertThing ( deque<Thing> & things, Thing thing, size_t index )
{
   deque<Thing>::iterator it = /* what do I do here? */
   things.insert ( it, thing );
}

I'm sure this is a very basic question, and I apologize for it. It's been a long time since I've used the STL, and I don't see anything in std::deque's member list that obviously does what I want. Thanks.