Genreic Double Linked List Using Templates
 

Generic Double Linked List

/* These are generic Functions for a Generic List

 * Note:-Only Functions not including a Menu and an Interface

 * You could use these Functions for your own Benefit*/

#include <iostream>

using namespace std;

template <class X> struct node{   //Template Structure

        X data;

        node* next;

        node* prev;

};



template <class Y> void insert_first(node<Y>** l,Y elem) 

{

        node<Y>* Q=new node<Y>();

        Q->data=elem;

        Q->prev=NULL;

        Q->next=*l;

        *l=Q;

}

template <class Y> void print_l(node<Y>* l)//Print the List

{

        while(l!=NULL)

        {

                cout<<l->data<<"   ";

                l=l->next;

        }

}

template <class type> int count(node<type>* l)//Count the List

{

        int counter=0;

        while(l!=NULL)

        {

                counter++;

                l=l->next;

        }

        return counter;

}



template <class type> void append(node<type>** l,type elem)

{

        if(*l==NULL)

                insert_first(&*l,elem);

        else

        {

                node<type>*temp=*l;

                node<type> *Q=new node<type>;

                Q->data=elem;

                while(temp->next!=NULL)

                {

                        temp=temp->next;

                }

                temp->next=Q;

                Q->prev=temp;

        }

}

template <class type> 

void insert_at_pos(node<type> **l,int pos,type elem)

{

        if(pos<=0||pos>count(*l))

        {

                cout<<"Invalid Position"<<endl;

                exit(1);

        }

        node<type>* Q=new node<type>;

        node<type>* temp=*l;

        int i=2;

        if(pos==1)

        {

                insert_first(&*l,elem);

        }

        else

        {

                while(temp!=NULL)

                {

                        if(pos==i)

                        {

                                Q->data=elem;

                                Q->next=temp->next;

                                Q->prev=temp;

                                temp->next=Q;

                        }

                        i++;

                        temp=temp->next;

                }

        }

}



int main(int argc, char** argv)

{

        node<int>* q=NULL;//Create Empty Pointer that Will point to the Head of the List

        insert_first(&q,2);

        insert_at_pos(&q,2,2);

        return 0;

}

If there is any critique about this code plz tell me about it to be careful in the next time i write any code .

Re: Genreic Double Linked List Using Templates
 

You wrote a bunch of C-style unsafe functions instead of a good C++ class List with comfortable and safe interface. Look at the class std::list as a model. Now these templates look like a steam-engine with microcontrolled whistle...

Re: Genreic Double Linked List Using Templates
 

Mr ArkM I didn't intend using classes but i was intending to try to use the (Generic Functions ) Definition not a Generic Class or something like that and in addition to that i wrote this code as an extension to the course that i am taking at college which is (Data Structures and Algorithm Analysis in C (not C++).

BTW thanx for your advice.

Re: Genreic Double Linked List Using Templates
 

I see. I think it's not the best problem area to try generic functions. You are trying to declare a family of related functions implemented some generic data structure. But it's exactly a class notion. Now your efforts demonstrated a disparity of a goal and tools.

When we need generic functions? We want a generic unit of functionality - for example, generic sort array operation...

Apropos, don't use by value parameters in program cases as in following code:

... append(node<type>** l,type elem) {

... Q->data=elem;

No need in argument copying, use references:

... append(node<type>** l,const type& elem) {

Yet another remark(s): print_l function requires operator << for template argument class. Why? There are lots of data classes without such operator but now you can't use them with your functions package. Avoid such names as print_l: simply look at print_l and print_1 (different;) ) names...

Re: Genreic Double Linked List Using Templates
 

Mr ArkM i'm very thankful for your interaction with me .
Could u plz explain your purpose cuz i tried it and it went to infinite loop while displaying random numbers (or maybe the addresses) and why we pass the reference of the element while u know in the structure up there
contains a variable of type X not a pointer of type X to receive the address ?.
Plz Explain your point Mr.ArkM . :$

Re: Genreic Double Linked List Using Templates
 

Try to insert val at pos 4 without insert val at pos 2..Is it work?..

Re: Genreic Double Linked List Using Templates
 

Please, present your modified code (with test main, of course).

Re: Genreic Double Linked List Using Templates
 

This is the modified function

template <class type> void append(node<type>** l,const type& elem)

{

        if(*l==NULL)

                insert_first(&*l,elem);

        else

        {

                node<type>*temp=*l;

                node<type> *Q=new node<type>;

                Q->data=elem;

                while(temp->next!=NULL)

                {

                        temp=temp->next;

                }

                temp->next=Q;

                Q->prev=temp;

        }

}

and this is the test in main

int main(int argc, char** argv)

{

        node<int>* q=NULL;//Create Empty Pointer that Will point to the Head of the List

        insert_first(&q,2);

        append(&q,5); //Here is the test

        print_l(q);

        system("PAUSE");

        return 0;

}

Re: Genreic Double Linked List Using Templates
 

Well, this code prints "Invalid position" then exit (it's a very bad solution: after exit() automatic class variables destructors are not called). You don't use modified append function. Moreover, passed by reference data argument can't raise new problems at all...

I have no time to debug your code from the beginning. Please, make a proper test plan, prepare test cases then ask help with the serious problems brief and clear description.

It's so simply to destruct your list via improper calls of these low-level functions. May this package debugging troubles help you to understand that all these low level operations must be incapsulated in the well-designed class ;)...