I'm trying to implement a Deque using smart pointers. However, I noticed that at the end of the program the Nodes of the Deque are not destructed properly.
Here is the code:
#include<iostream>
#include<memory>
class Node
{
int value;
std::shared_ptr<Node> next = nullptr;
std::shared_ptr<Node> prev = nullptr;
public:
Node() = default;
Node(int val): value(val) {}
~Node()
{
std::cout << "Destructor of node: " << value << std::endl;
}
friend class Deque;
};
class Deque
{
using pointer = std::shared_ptr<Node>;
pointer head = nullptr; // pointer to the first element of the queue
pointer tail = nullptr; // pointer to the last element of the queue
public:
Deque() = default;
~Deque(){ std::cout << "Dequeue destructor" << std::endl; }
bool is_empty()
{
if (head == nullptr && tail == nullptr )
return true;
else
return false;
}
void push_back(const pointer& val)
{
if (is_empty())
{
head = val;
tail = val;
}
else
{
val->prev = tail;
tail->next = val;
tail = val;
}
}
};
int main()
{
Deque DEQ;
auto node1 = std::make_shared< Node >(1);
auto node2 = std::make_shared< Node >(2);
auto node3 = std::make_shared< Node >(3);
DEQ.push_back(node1);
DEQ.push_back(node2);
std::cout << "Use count node1 = " << node1.use_count() << std::endl;
std::cout << "Use count node2 = " << node2.use_count() << std::endl;
std::cout << "Use count node3 = " << node3.use_count() << std::endl;
return 0;
}
The output is the following:
Use count node1 = 3
Use count node2 = 3
Use count node3 = 1
Destructor of node: 3
Dequeue destructor
when I push the node1
and node2
into the Deque, they are not destructed at the end of the program, while node3
is correctly destructed.
I assume the problem is that the reference count of node1
and node2
is equal to 3. Do you know how I can change my implementation in order to solve this problem? Thanks.
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