class A {
public:
    void doSomething() {}
}
boost::unordered_map<int, boost::intrusive_ptr<A>> m;
m.insert(0, new A());
m.insert(1, new A());
m.insert(2, new A());

// later...
std::vector<boost::intrusive_ptr<A>> f;
boost::unordered_map<int, boost::intrusive_ptr<A>>::iterator i;

i = m.find(0);
f.push_back(i->second);
i = m.find(1);
f.push_back(i->second);
i = m.find(2);
f.push_back(i->second);

// and then do operations on f:
for(size_t i = 0; i < f.size(); ++i) {
    f[i].doSomething();
}

class A {
public:
    void doSomething() {}
}
boost::ptr_unordered_map<int, A> m;
m.insert(0, new A());
m.insert(1, new A());
m.insert(2, new A());

// later...
boost::ptr_vector<A> f;
boost::ptr_unordered_map<int, A>::iterator i;

i = m.find(0);
f.push_back(i->second);
i = m.find(1);
f.push_back(i->second);
i = m.find(2);
f.push_back(i->second);

// and then do operations on f:
for(size_t i = 0; i < f.size(); ++i) {
    f[i].doSomething();
}