Question

I want to know if this code is safe and doesnt have any undefined behavior.

 QueueMap::const_iterator it = m_3playersQueue.find(s->m_GameCode);
 if(it == m_3playersQueue.end())
 {
     std::deque<Session*> stack;
     stack.push_back(s);

     m_3playersQueue[s->m_GameCode] = stack;
     return;
 }

 const_cast<std::deque<Session*>&>(it->second).push_back(s);

 QueueMap is of type std::tr1::unordered_map< uint32, std::deque<Session*> >

Answer 1

Yes, it is safe. Even if a const_iterator is different from an iterator, the objects in the map are the same. As long as all the map contents were created as mutable std::deque<Session*> objects, it’s OK to cast the constness away.

Of course, it’s possible you’re violating some invariant the constness was meant to convey, but that’s possible with any const_cast taken in isolation.