Queues and copying

[Erdrigard]

Hi. I'm having trouble with, uh, queues and copying.

Here's some code:

template <class Type>
const queueType<Type>& queueType<Type>::operator=(const queueType<Type>& q)
{
      if (this != &q)
         copyQueue(q);
         
      return *this;
}

template <class Type>
void queueType<Type>::copyQueue(const queueType<Type>& queue)
{
     delete [] list;
     maxQueueSize = queue.maxQueueSize;
     queueFront = queue.queueFront;
     list = new Type[maxQueueSize];
     
     for (int s = 0; s < maxQueueSize; s++)
        list[s] = queue.list[s];
}

template <class Type>
void queueType<Type>::queueType(const queueType<Type>& queue)
{
    list = NULL;
    copyQueue(queue);
}

Here are the overloaded assignment operator, utility function to copy the data and a copy constructor. I'm guessing the culprit is in one of the above.

As for the problem, here's main:

int main(int argc, char *argv[])
{
    queueType<int> queue;
    queueType<int> q2;
    
    int x, y;
    
    queue.initQueue();
    x = 4;
    y = 5;
    queue.addQueue(x);
    queue.addQueue(y);
    x = queue.front();
    queue.deleteQueue();
    queue.addQueue(x + 7);
    queue.addQueue(19);
    queue.addQueue(x);
    queue.addQueue(y - 4);
    
    q2 = queue;
    
    while (!queue.isQueueEmpty())
    {
          cout << queue.front() << " ";
          queue.deleteQueue();
          }
    
    cout << endl;
    cout << "q2 elements: ";
    
    while (!q2.isQueueEmpty())
    {
          cout << q2.front() << " ";
          q2.deleteQueue();
          }
    
    cout << endl;
    
    system("PAUSE");
    return EXIT_SUCCESS;
}

Other functions act as their name implies. Can get code for those if needed. Here's the output.

4 5 3998839 19 3998832
q2 elements: 
Press any key to continue...

The question: why wasn't the queue from queue copied to q2 even though q2 was assigned to queue?

Oh, and another thing, what's with the junk numbers in the output? Looks like it's returning an address. Seems to react this way when I put a variable into the queue (like (y-4) for example).

[ne555]

post addQueue, front, deleteQueue. The copy seems fine, (check the value of maxQueueSize)

[Erdrigard]

Sure. Here's front(), addQueue() and deleteQueue() respectively.

template <class Type>
Type queueType<Type>::front() const
{
   assert(!isQueueEmpty());
   return list[queueFront];
}

template <class Type>
void queueType<Type>::addQueue(const Type& newElement)
{
     if(!isQueueFull())
     {
        queueRear = (queueRear + 1) % maxQueueSize;   //use mod operator to advance queueRear because array is circular
        count++;
        list[queueRear] = newElement;
        }
    else
        cout << "Can't add to a full queue." << endl;
}

template<class Type>
void queueType<Type>::deleteQueue()
{
     if (!isQueueEmpty())
     {
        count--;
        queueFront = (queueFront + 1) % maxQueueSize;            
        }
     else
         cout << "Cannot remove from an empty queue." << endl;
}

[ne555]

Sorry, I didn't note this the first time:
void queueType<Type>::queueType(const queueType<Type>& queue) Constructors don't have return type
const queueType<Type>& queueType<Type>::operator=(const queueType<Type>& q) Shouldn't return a const reference (the idea is that you could do A = B = C = ...;)
In copyqueue I think that you need to copy queueRear and count too.

Also it seems weird that you increment Rear before adding the new element (so Rear starts in -1). So I used count to check for empty or full.

[Erdrigard]

I tried out all those suggestions, to no avail. The constructor one struck me as odd since the compiler accepted it. Thanks for the suggestions, though.