Очередь - цикл.список

#include <iostream>

using namespace std;

struct queue_node
{
    queue_node* next;
    int data;
};
typedef queue_node* queue;

void InitQueue (queue &q)
{
    q = nullptr; // q = NULL;
}

void PutQ (queue &q, int data)
{
    queue new_node = (queue)malloc(sizeof(queue_node));
    new_node->data = data;

    if (q == nullptr)
    {
        new_node->next = new_node;
    }
    else
    {
        queue head = q->next;
        q->next = new_node;
        new_node->next = head;
    }
    q = new_node;
}

int GetQ(queue &q)
{
    if (q != nullptr)
    {
        queue p = q->next;
        int data = p->data;

        if (p == q) q = nullptr;
        else
        {
            q->next = p->next;
        }

        free(p);
        return data;
    }
    else
    {
        cout << "Queue is empty" << endl;
        return -1;
    }
}

int main()
{
    queue q;
    InitQueue(q);
    PutQ(q, 1);
    PutQ(q, 2);
    PutQ(q, 3);
    cout << GetQ(q) << ' ' << GetQ(q) << ' ' << GetQ(q) << ' ' << endl;
    return 0;
}