Difference between boost ptr containers and normal containers?

Question

What is the difference between using boost ptr containers and containers that contains smart pointers?

class A {} 

// ptr containers:
boost::ptr_unordered_map<int, A> p;

// containers:
boost::unordered_map<int, boost::intrusive_ptr<A>> m;

I'm rolling back the latest revision. If you have a new question, [ask a new question](http://stackoverflow.com/questions/ask). It's bad form here to edit a question to invalidate existing answers. — Drew Dormann, Jul 25 '14 at 18:04

score 1 · Accepted Answer · answered Jul 25 '14 at 17:11

1

boost::ptr_unordered_map does not have the reference-counting overhead that would be incurred in a container of boost::shared_ptr<A>

It also does not require the additional A object interface that boost::intrusive_ptr<A> demands.

That makes it a good solution for managing heap-allocated objects that do not require reference counting of the contained objects.

answered Jul 25 '14 at 17:11

Drew Dormann

Just curious here, why do you think they didn't make a template specialization for `boost::unordered_map>`? – Nick Strupat Jul 25 '14 at 17:14
@NickStrupat I suspect it's because that type may or may not require reference counting for the shared pointers inserted in the container. It's not implicitly known if other pointers to the objects exist elsewhere. – Drew Dormann Jul 25 '14 at 17:17
When should I use reference counting? – Zilberman Rafael Jul 25 '14 at 17:39
@DrewDormann see my update. Can I change the containers to use ptr containers in my case? – Zilberman Rafael Jul 25 '14 at 18:01

1 Answers1