Template Queue

[khal]

#ifndef QUEUE_H
#define QUEUE_H
#include <cstddef>

template<class T>
class Queue
{
    public:
        Queue();
        bool isEmpty();
        void enqueue(T data);
        void dequeue();
     

    private:
        struct Node{
            T date;
            Node *next;
        };

        Node *frontPtr;
        Node *backPtr;
        int count;

};

#endif // QUEUE_H 

#include "Queue.h"
#include <iostream>
using namespace std;


template<class T>
Queue<T>::Queue(): frontPtr(NULL), backPtr(NULL), count(0)
{
}

template<class T>
bool Queue<T>::isEmpty(){
    return(count == 0);
}

template<class T>
void Queue<T>::enqueue(T data){
    Node *newOne = new Node;
    newOne->date = data;
    newOne->next = NULL;
    if(isEmpty()){
        frontPtr = newOne;
    }
        else{
            backPtr->next = newOne;
        }
        backPtr = newOne;
        count++;
}

template<class T>
void Queue<T>::dequeue(){
    if(isEmpty()){
        cout << "Nothing inside" << endl;
    }
        else{
            Node *temp = frontPtr;
            if(frontPtr == backPtr){
                frontPtr = NULL;
                backPtr = NULL;
            }
            else{
                frontPtr = frontPtr->next;
            }
            delete temp;
            count--;
        }
}

#include <iostream>
#include <string>
#include "Queue.h"
using namespace std;


int main()
{
    Queue<int> bo;
    int x = 2;
    bo.enqueue(x);
    return 0;
}

I do not understand why I get this error as an output. Any help would be great.

obj\Debug\main.o||In function `main':|
C:Queue\main.cpp|9|undefined reference to `Queue<int>::Queue()'|
C:Queue\main.cpp|11|undefined reference to `Queue<int>::enqueue(int)'|
||=== Build finished: 2 errors, 0 warnings ===|

[Baelix]

Even though this may not solve the problem, humor me by putting your "using namespace std;" in your header file instead of implementation file.

[firedraco]

^That's not the problem, and you shouldn't be using anything in your header files anyway.

The issue that all your template definitions must be present in the *header* file, not a related .cpp file.

[khal]

Baelix, As far as I know the using namespace std is not require in a .h file since I am not creating an abstract class... I tried it any way did not make a difference

[Baelix]

Fire nailed it. Completely forgot the rules that go along with templating :P

Instead of having 2 seperate files (1 .cpp and 1 .h) put all of your implementation into your header file. I won't divulge where or how; that's easy enough to google :P

[khal]

Thank you firedraco,Baelix Its weird that the template definition cannot be in .cpp file.

[shacktar]

Well you can separate template implementation from declaration if you know in advance what specific instantiations of the template your program will use and place them in a .cpp file.

http://www.parashift.com/c++-faq-lite/templates.html#faq-35.15

You can take the code you had in the OP and add this line to the end of Queue.cpp

template class Queue<int>;

and it should compile and link for you.

[ne555]

As far as I know the using namespace std is not require in a .h file since I am not creating an abstract class...

Quite a misconception you have. Namespaces are used to avoid name collision.
The standard c++ classes and functions are inside the std namespace.
If you want to use them, then you need to qualify them. By instance std::ostream.

You can use using to avoid that prefix thing. However the effect is as if the function were declared in the global namespace.
So using in a header defeats the purpose of namespaces.