Hello all,
So I'm working on this simple program with a Queue class template that is publicly derived from the abstract base class CharQueue.
The only problem is that I keep getting hit with the error "expected class name before '{' token". The reason I don't understand this is that I never got this error until I made the class a template, but I can't see how it being a template now should affect that.
Anyways, here's the code (the error is at line 8/9:
queueTemplate.h containing Queue class:
#include "CharQueueTemplate.h"
#include <cassert>
#include <new>
#include <cstddef>
using namespace std;
template <typename T> class Queue : public CharQueue
{
private:
struct qNode {
T element;
qNode *next;
};//end qNode
qNode *front;
qNode *back;
public:
Queue();//default constructor
Queue(const Queue<T>& q);//copy constructor
virtual ~Queue();//destructor
virtual bool isEmpty() const;//checks to see if the queue is empty
virtual void enqueue(const T & value);//places value at the back of the queue (prior to the head pointer in this case)
virtual void dequeue();//removes the front value from the queue
//virtual void dequeue(T& head);
virtual T getFront() const;
};//end Queue
template <typename T> Queue<T>::Queue()
{
back= NULL;
front = NULL;
}//end default constructor
template <typename T> Queue<T>::Queue(const Queue & aq)
{
if(!aq.isEmpty())
{
qNode *original = aq.front;
qNode *newhead = new qNode;//points to the head of the list
newhead->element = original->element;
newhead->next = newhead;
front = newhead;
qNode *nCurrent = newhead;
//qNode *temp = new qNode;
while(original != aq.back)
{
original = original->next;
nCurrent->next= new qNode;
nCurrent = nCurrent->next;
nCurrent->element = original->element;
nCurrent->next = NULL;
back=nCurrent;//possible error
}//end while
}//end if
}//end copy constructor
template <typename T> Queue<T>::~Queue()
{
while(!isEmpty())
{
dequeue();
}
}//end destructor
template <typename T> bool Queue<T>::isEmpty() const
{
return (front == NULL);
}//end isEmpty
template <typename T> void Queue<T>::enqueue(const T& value)
{
try
{
//make new node
qNode *temp = new qNode;
temp->element = value;
temp->next = NULL;
if(isEmpty()) {
front = temp;
}//end if
else
back->next = temp;
back = temp;
}//end try
catch (bad_alloc e)
{
throw string("Memory cannot be allocated.");
}//end catch
}//end enqueue
template <typename T> void Queue<T>::dequeue()
{
if(!isEmpty())
{
qNode *temp = front;
if(front == back)
{
front = NULL;
back = NULL;
}
else
{
front = front->next;
temp->next = NULL;
delete temp;
}//end else
}//end if
}//end dequeue
template <typename T> T Queue<T>::getFront() const
{
if(!isEmpty())
{
return front->element;
}//end if
}//end getFront
//end q.hAnd CharQueueTemplate.h which contains the abstract base class CharQueue:
template <typename T>
class CharQueue
{
public:
virtual bool isEmpty() const = 0;
virtual void enqueue(const T & newItem) = 0;
virtual T dequeue(void) = 0; // dequeue an item and return its value
virtual T getFront(void) const = 0; // return the value of the first item in the queue (but do not dequeue it)
};Any input input anyone has on this would be greatly appreciated, since this error has me stumped right now.
