Use of structure pointer with boost::mutable_queue

I have worked on this for a few hours and finally made the whole thing work. Few article explained about either comparators with pointers or use of structure with mutable_queue, and I decided to dig the source code of STL directly. The following code is the gist of what I got from the somewhat long search:

1. #include <iostream>
2. #include <stdlib.h>
3. #include <vector>
4. #include <boost/pending/mutable_queue.hpp>
5.  
6. using namespace boost;
7. using namespace std;
8.  
9. struct node {
10.   int id;
11.   int value;
12. };
13.  
14. struct compare_node: public std::binary_function<struct node*, struct node*, bool>{
15.   bool operator()(struct node *const& n1, struct node *const & n2) const {
16.     return (n1->value < n2->value);
17.   }
18. };
19.  
20. struct node_identity_property_map : public boost::put_get_helper<std::size_t, node_identity_property_map> {
21.   inline std::size_t operator[](struct node *const & v) const { return v->id; };
22. };
23.  
24. typedef mutable_queue<struct node *, vector<struct node*>,
25.                       compare_node, node_identity_property_map> mutable_queue_t;
26.  
27. #define SIZE_ID_SPACE 10
28.  
29. int main() {
30.   mutable_queue_t q(SIZE_ID_SPACE, compare_node(), node_identity_property_map());
31.  
32.   struct node nodes[10];
33.   cout << "putting items......" << std::endl;
34.   for (int i = 0; i < SIZE_ID_SPACE; i++) {
35.     nodes[i].id = i;
36.     nodes[i].value = i;
37.     cout << "id=value=" << i << endl;
38.     q.push(&nodes[i]);
39.   }
40.  
41.   for (int i = 0; i < SIZE_ID_SPACE; i++) {
42.     nodes[i].value = rand();
43.     q.update(&nodes[i]);
44.   }
45.  
46.   cout << std::endl << "retrieving items......" << std::endl;
47.   for (int i = 0; i < SIZE_ID_SPACE; i++) {
48.     std::cout << "id: " << q.top()->id << "\t" << q.top()->value << std::endl;
49.     q.pop();
50.   }
51.   return 0;
52. }