Thread: Queue with templates

So I've been designing a queue. I finished the base of it and implemented templates. The reason I started this project was to learn about templates, and get some more practice in this area and others such as pointers and linked-lists. So I have no idea if I'm doing it correctly really. It seems to work, but theres a few problems. Firstly if I create a Queue object of type <char> like so:

Code:

Queue<char> q;

I can't pass in a character in this format:

Code:

q.pop('a');

It needs to be like this:

Code:

q.pop("a");

Yes, ' ' is for characters, " " is for strings, so why won't it let me use ' '? I'm thinking that I maybe should change it so that pop only accepts a reference to something, so that would eliminate the risk of that (I'm just guessing to be honest).

Another thing, if I specify a string like such:

Code:

q.pop("Hello");

It only pops the first letter of that string. So the output would be H. But if I declare the type of the object <string>, and use the <string> library, then it will print a whole string . So those are the problems I have so far, but I also have a question. You see, the return type of pop is a pointer of type T, so, I obviously need to assign the returned pointer to my own pointer to get the values of the returned pointer. The thing is, I don't know of a way to match the type of my pointer to the type of the Queue object without doing it manually in the declaration of my pointer. I'll give an example because it's not a great explanation:

Code:

int main() {
	Queue<float> q;
	float * data = 0;
	q.push(3.5);
	q.push(2.7);
	q.push(1.5);
	q.push(6.5);
	while (q.getCount() > 0) {
	float * data = q.pop();
	cout << *data << endl;
	}
}

See how I've declared a pointer named data, that points to type float? Well, it would be a lot more convenient for me (I'm not sure if this is even possible yet) if I could have it as a pointer to return type of the same as Queue, which in this example is float. So instead of float * data = 0;, Is there a way to make it something like "Queues-template-type * data" so I don't have to specify what return type the data pointer holds? Anyways I'm not great at explaining this stuff :P So hopefully you know what I'm talking about. Here's the rest of the code.

Code:

#include <iostream>
#include <string>

using std::cin;
using std::cout;
using std::endl;
using std::string;

template <class T>
class Node {
public:
	T * data;
	Node<T> * next;
	Node<T> * prev;
	Node();
};

template <class T>
class Queue {
public:
	Queue();
	~Queue();
	void push(T data);
	void push(T * data);
	T * pop();
	inline int getCount() { return count; }

private:
	Node<T> * head;
	Node<T> * tail;
	Node<T> * forward;
	Node<T> * backward;
	int count;
};

template <class T>
Node<T>::Node() {
	next = NULL;
	prev = NULL;
	data = new T;
}

template <class T>
Queue<T>::Queue() {
	head = NULL;
	tail = NULL;
	forward = NULL;
	backward = NULL;
	count = 0;
}

template <class T>
Queue<T>::~Queue() {
	Node<T> * n = tail;
	Node<T> * del;
	while ( n ) {
		del = n;
		n = n->prev;
		delete del;
	}
}

template <class T>
void Queue<T>::push(T data) {
	push(&data);
}

template <class T>
void Queue<T>::push(T * data) {
	if (!head) {
		head = new Node<T>;
		*head->data = *data;
		head->next = NULL;
		head->prev = NULL;
		tail = head;
	}
	else {
	tail->prev = tail;
	tail->next = new Node<T>;
	tail = tail->next;
	*tail->data = *data;
	tail->next = NULL;
	}
	count++;
}

template <class T>
T * Queue<T>::pop() {
	if (head == NULL) {
		return 0;
	}
	else if (head == tail->prev) {
		T * data = head->data;
		delete head;
		count--;
		return data;
	}
	else {
		T * data = head->data;
		head = head->next;
		count--;
		return data;
	}
};

int main() {
	Queue<float> q;
	float * data = 0;
	q.push(3.5);
	q.push(2.7);
	q.push(1.5);
	q.push(6.5);
	while (q.getCount() > 0) {
	float * data = q.pop();
	cout << *data << endl;
	}
}

Any suggestions/advice is welcome, like I said, I'm not familiar with templating, so I'm not certain that I'm doing it correctly (although it does work which is promising).

Thanks a lot!

Edit: Oh and if you're around here Laserlight you'll see that I implemented a linked-list, not sure if you remember but you gave me that suggestion not long ago hehe