Implementing an Enqueue At Offset Method for a CircularQueue - c++

Question

I am currently working on a project to simulate Traffic Flow around a Roundabout and in order to do this I have built 2 data structures "LinearQueue" and "CircularQueue" both implemented using Linked List struct nodes.
My CircularQueue class has methods to enqueue and dequeue as is typical of any circular queue type structure, however as I have 4 (well 8 actually given roads going in both directions) LinearQueue objects that will need to link at quarter capacity intervals of the CircularQueue (roundabout) object I require a method to enqueue items at an offset from the rear or front of the queue and I am unsure of how to implement this properly.
Here is my CircularQueue::enqueue(Type) method:
Type enqueue(Type& item) {
// if the currentSize is greater than the maximum allowed capacity,
// throw a CircularQueueException
if (this->currentSize == this->maxCapacity) {
throw CircularQueueException("Circular queue is full, cannot enqueue any more objects!");
}
// if the front of this CQ object is null, assign first element of circularQueue array to
// front of queue and set the rear to the front (single-element queue)
if (this->front == 0) {
this->front = this->circularQueue[0];
this->front->head = item;
this->rear = this->front;
}
// else if the front is not-null, assign the tail of the rear of this CQ object
// to a new CQNode with head = item, and shift the new rear to tail of old rear
else {
this->rear->tail = new CQNode(item);
this->rear = this->rear->tail;
// if the currentSize of the queue is 1 less than the maximum capacity, then
// point to tail of the rear to the front of the queue
if (this->currentSize == (this->maxCapacity - 1))
this->rear->tail = this->front;
}
// increment the currentSize of this CircularQueue instance by 1 indicating enqueue successful
this->currentSize++;
return item;
}
where currentSize and maxCapacity are integer field variables storing the current filled queue size and maximum allowed capacity, respectively. Front and rear are pointers to the following node structure:
struct CQNode {
Type head;
CQNode* tail;
CQNode() {
//this->head = 0;
this->tail = 0;
}
CQNode(Type& head, CQNode* tail = 0) {
this->head = head;
this->tail = tail;
}
};
And Type is a typename given in the template of the class.
I currently only have the following for my offset enqueue method:
Type enqueue(Type& item, int offset) {
// if the offset given is 0, then simply call overloaded enqueue with just the item
if (offset == 0) {
return enqueue(item);
}
Type* itemPtr = &item;
if (itemPtr == 0) {
throw std::invalid_argument("Item to be enqueued onto Circular Queue cannot be null!");
}
if (this->currentSize == this->maxCapacity) {
throw CircularQueueException("Circular queue is full, cannot enqueue any more items.");
}
}
I'm just struggling to find where to start with the method, as I can see plenty of problems with null pointers by enqueuing and dequeuing objects at different offsets in my CircularQueue.