Traversing (and populating where nodes don't exist) a hierarchical structure in a std::map

PopulateHierarchicalStruct

// Traversing (and populating where nodes don't exist) a hierarchical structure:

struct AllocStackIdMapEntry
{
    std::map<int, AllocStackIdMapEntry*> children;
};


{
    std::vector<int> callstack;

    AllocStackIdMapEntry *ptr = &root;

    int i=0;
    while (i<size) {
        int id = callstack.at(i++);
        //printf("Finding child with id=%d, ptr now %#010x\n", id, ptr);
        std::map<int, AllocStackIdMapEntry*>::iterator lb = ptr->children.lower_bound(id);
         
        if (lb != ptr->children.end() && !(ptr->children.key_comp()(id, lb->first)))
        {   // key already exists
            ptr = lb->second;
        } else {
            // the key does not exist in the map, add it
            AllocStackIdMapEntry *newEntry = new AllocStackIdMapEntry();
            ptr->children.insert(lb, std::map<int, AllocStackIdMapEntry*>::value_type(id, newEntry));
            ptr = newEntry;
        }
    }
}