prob making class template

[SteroidalPsycho]

I can't figure out how to make a class template out of a class that i have already defined. Could someone explain to me how templates are implemented? My class code is below and I just need to know how to make it a template class with templated functions. Thanks!!

class iVec
{
public:
	iVec();//constructor
    int at(int);
    int size();
    void resize(int);
    void push_back(int);
    void pop_back();
	void print();

private:
	Node *iNode;
	int maxSize;
};
iVec::iVec(){
	iNode=0;
}//end constructor

//at function returns the index of a value
//that the programmer passes to the funtion.
int iVec::at(int n){
	Node *current=m;
	for(int count = 0; count<size();count++){
		if(n==current->data)
			return count;
		else
			current=current->next;
	}
	return NULL;
}//end at()
//function size() returns the number of elements in the list.
int iVec::size(){
	Node *temp=m;
	int count = 0;
	while(temp!=NULL){
		temp=temp->next;
		count++;
	}
	return count;
}
//Function resize() resizes the container.
//If the new size is less than the current
//size, then the extra nodes are discarded.
//If it is larger, then empty nodes are
//added to the end of the container.
void iVec::resize(int n){
	cout<<"The container is being resized to "<<n<<" elements."<<endl<<endl;
	Node *temp;
	temp = m;
	//if n > size of the container
	//then make new empty nodes until
	//size==n
	if(n>size()){
		while(temp->next!=NULL&&size()<=n){
			temp=temp->next;
			if(temp->next==NULL)
				temp->next=new Node;
		}//end while
	}//end outside if
	//if n<size() then delete the values
	//past n.
	if(n<size()){
		while(temp->next!=NULL&&size()>n){
			temp=temp->next;
			if(temp->next==NULL){
				pop_back();
				temp=m;
			}//end inside if
		}//end while
	}//end if
}//end resize()

//Function push_back adds a node to
//the end of the container. If the 
//list is empty, then a new node is
//created with the value n.
void iVec::push_back(int n){
	Node *temp,*temp2;
	//if container is empty then
	//initiate the first node value.
	//with the user defined value.
	if( m == NULL )
    {
      m = new Node;
      m->data = n;
      m->next = NULL;
    }//end if
	//else add a node of the user
	//defined value to the end of 
	//the container
    else
    {
		temp = m;
		while( temp->next != NULL ){
			temp = temp->next;
		}//end while
		temp2 = new Node;
		temp2->data = n;
		temp2->next = NULL;
		temp->next = temp2;
	}//end else
	cout<<"The value "<<n<<" was added to the end of the container.";
	cout<<"\n";
}//end push_back()
//Function pop_back deletes the last value
//in the container. If no values exist in
//the list, a message is printed to the user
//and the function is exited.
void iVec::pop_back(){
	Node *current = m;
	Node *temp;
	//if the first node is empty then the program
	//notifies the user that the container is empty
	//and returns.
	if(current==NULL){
		cout<<"The container is empty.";
		return;
	}//end if
	//while deletes the last node in the list 
	while(current->next!=NULL){
		temp = current;
		current=current->next;
	}
	temp->next = NULL;
	delete current;
	cout<<"The last value in the container has been removed."<<endl<<endl;
	
}//end pop_back()
//Function print() prints all values
//in the container to the screen.
void iVec::print(){
	Node *temp;
 	cout<<endl<<"These are the container's elements:";
	for( temp = m ; temp != NULL ; temp = temp->next ){
		if(temp->data!=NULL)
			cout<<endl<<temp->data;
	}//end for
	cout<<endl<<endl;
}//end print() 

[Galik]

I recommend starting with a few small classes to get how it works.

For this I think you are going to have to template your Vec and your Node classes:

template<typename T>
struct Node
{
    T data;
    Node<T>* next;
};

template<typename T>
class Vec
{
    Node<T>* node;
public:
    void push_back(const T& value);
    T& at(int);
};

Simply put T wherever the type you want to replace needs to be.

[guestgulkan]

Pretty much agree with what Galik said.


On another matter, I think this function is logically incorrect if NULL has been defined to have the value 0 (zero):

//at function returns the index of a value
//that the programmer passes to the funtion.
int iVec::at(int n){
	Node *current=m;
	for(int count = 0; count<size();count++){
		if(n==current->data)
			return count;
		else
			current=current->next;
	}
	return NULL;
}//end at() 

[jsmith]

Not to mention that it almost does the exact opposite of what vector<>::at() does, so will probably
be confusing/surprising to the user.

[SteroidalPsycho]

Ok I just don't get how the function templates are made with the implementations. I'm severely confused by templates I don't know where to start to ask questions cause the concept kinda makes since I just don't get all the syntax and passing T& values to the functions. Does that make a little sense?

[jsmith]

Perhaps start with a simple example.

Suppose I had a Point class:

struct Point {
    Point( int x, int y ) : x( x ), y( y ) {}
    int x, y;
};

and now I want to make another Point class that uses doubles instead of ints. I could:

struct PointD {
    PointD( double x, double y ) : x( x ), y( y ) {}
    double x, y;
};

Notice that all I did was rename the class (struct) and replace all "int" with "double".

Or, I could use a template:

template< typename T >
struct Point {
    Point( T x, T y ) : x( x ), y( y ) {}
    T x, y;
};

Now Point<int> makes a struct named Point with x and y defined as int, and
Point<double> makes a struct named Point with x and y defined as double.

This is all templates really are.

If I want to move the implementation of the constructor outside the class
(struct), then I write it like:

template< typename T >
struct Point {
    Point( T x, T y );
    T x, y;
};

template< typename T >
Point<T>::Point( T x, T y ) : x( x ), y( y ) {}

[SteroidalPsycho]

So i'm getting an error on line 13 of the code below. can you not do what i did with *m in templates? To be honest, I didn't really understand what that actually did. I just know that I used *m whenever I wanted to access the first node in the list. But when i templated the class, I got error: syntax error : missing ';' before '*'

and also this error: missing type specifier - int assumed. Note: C++ does not support default-int

template<class T>
class Node
{
public: 
    T data;
    Node<T>* next;
	
	Node()
    {
    data=0;
    next=0;
    }//end Node()
}*m;//end class Node 

[Galik]

What is the *m for? It looks like you are declaring a global Node *. That's not a great thing to do anyway. You would probably be better making m a member of Vec.

[kempofighter]

Okay - what you are doing makes no sense. You have now made the Node a template. If you want to instantiate a node or a pointer to a node then you must write either:

// Where typename could be int, double, or whatever.
[code]Node<typename> theNodeObject;  
Node<typename>* theNodePointer;

[/code]

Did you read the template tutorial on this website? I'd also like to point out that it is not a very good idea to create something called iVec and then make it work like a linked list. vectors are not linked lists in C++. Those names have specific meanings to people who use the STL and what you have done will be very confusing to most users who know the STL.

[kempofighter]

If you really want to learn C++ and how templates work you'd be better off writing a program that uses the STL instead of trying to reinvent the wheel. Take a look at this.
http://cplusplus.com/forum/articles/10879/