Cant head insert on doubly linked list

aciarlillo · 09-15-2005, 06:27 PM

Okay, this is my first time working with doubly linked lists and I can't get past the first thing... doing a head insert.

here is my code for the insert:

Code:

template <class T>
void Dlist<T>::front_insert(const T& entry)
{
     if(head == NULL)
             head = new Dnode<T>(entry);
             
     Dnode <T> * temp;
     temp = new Dnode<T>(entry);
     temp->next = head;
     head->prev = temp;
     head = temp;
}

the biggest problem im having is linking the new node so it has a previous pointer at NULL and a 'next' pointer at the node that was originally the head. Then I need to set the previous node of what was the head to the new head. consufing?

Here is my Dlist.h:

Code:

#include "Dnode.h"

#include <iostream>
#include <string>

template <class T>
class Dlist{

  public:
         Dlist();
         Dlist(const Dlist& other);
         ~Dlist();
  /*      
   void list_clear(Dnode<T>*& head_ptr);
   void list_copy(const Dnode<T>* source_ptr, Dnode<T>*& head_ptr, Dnode<T>*& tail_ptr);
   std::size_t list_length(const Dnode<T>* head_ptr);
   void rear_insert(Dnode<T>* tail_ptr, const T& entry);
   void rear_remove(Dnode<T>*& tail_ptr);
   void front_remove(Dnode<T>*& head_ptr);
  */
   void front_insert(const T& entry);
 
  
 private:
          Dnode<T>* head;
          Dnode<T>* tail;
};

#include "Dlist.template"

and here is Dnode as well just in case:

Code:

template <class T>
class Dnode{

  public:      
  Dnode(T d =  T(), Dnode *n = NULL, Dnode *p = NULL){datafield = d; link_next = n; link_prev = p;}
  
  T& data(){return datafield;}
  Dnode * next(){return link_next;}
  Dnode * prev(){return link_prev;}

  void set_data(T d){datafield = d;}
  void set_link(Dnode * n = NULL, Dnode * p = NULL){link_next = n; link_prev = p;}
   
 private: 
            T datafield;
            Dnode * link_next;
            Dnode * link_prev;
};

i would really appreciate any instruction on this, I have the idea of what it is supposed to do but I think I am missing some fundamental knowledge in trying to implement this.
thanks,
-ac

Daved · 09-15-2005, 06:58 PM

>> the biggest problem im having is linking the new node so it has a previous pointer at NULL and a 'next' pointer at the node that was originally the head. Then I need to set the previous node of what was the head to the new head. consufing?

The code you post does all that except the part about setting the new node's previous pointer to null.

Also, don't forget to leave the function if the original head is null after you create the new head.

aciarlillo · 09-16-2005, 12:14 AM

i keep getting this error in my code:

67 C:\Dev-Cpp\240c1\Dlist.template invalid use of member (did you forget the `&' ?)
68 C:\Dev-Cpp\240c1\Dlist.template invalid use of member (did you forget the `&' ?)

aciarlillo · 09-18-2005, 10:34 AM

okay still looking for some help on this... i am getting the above two errors on these two lines of code:

Code:

temp->next = head;
head->prev = temp;

those two lines are from a function which can be seen in its entirety in the first post.

thanks

dwks · 09-18-2005, 11:31 AM

Code:

temp->next = head;
head->prev = temp;

Well, first of all, next and prev are functions:

Code:

public:
// ...
  Dnode * next(){return link_next;}
  Dnode * prev(){return link_prev;}
// ... 
 private: 
            Dnode * link_next;
            Dnode * link_prev;

You want something like

Code:

temp->setnext(head);
head->setprev(temp);

Where setnext() is public and declared as

Code:

void setnext(Dnode *n) {link_next = n;}

setprev() would be similar.

09-15-2005, 06:58 PM	#2
Daved Registered User Join Date: Jan 2005 Posts: 7,252	>> the biggest problem im having is linking the new node so it has a previous pointer at NULL and a 'next' pointer at the node that was originally the head. Then I need to set the previous node of what was the head to the new head. consufing? The code you post does all that except the part about setting the new node's previous pointer to null. Also, don't forget to leave the function if the original head is null after you create the new head.
Daved is offline

09-16-2005, 12:14 AM	#3
aciarlillo Registered User Join Date: Apr 2005 Posts: 29	i keep getting this error in my code: 67 C:\Dev-Cpp\240c1\Dlist.template invalid use of member (did you forget the `&' ?) 68 C:\Dev-Cpp\240c1\Dlist.template invalid use of member (did you forget the `&' ?)
aciarlillo is offline

09-18-2005, 10:34 AM	#4
aciarlillo Registered User Join Date: Apr 2005 Posts: 29	okay still looking for some help on this... i am getting the above two errors on these two lines of code: Code: temp->next = head; head->prev = temp; those two lines are from a function which can be seen in its entirety in the first post. thanks
aciarlillo is offline

09-18-2005, 11:31 AM	#5
dwks Frequently Quite Prolix Join Date: Apr 2005 Location: Canada Posts: 7,698	Code: temp->next = head; head->prev = temp; Well, first of all, next and prev are functions: Code: public: // ... Dnode * next(){return link_next;} Dnode * prev(){return link_prev;} // ... private: Dnode * link_next; Dnode * link_prev; You want something like Code: temp->setnext(head); head->setprev(temp); Where setnext() is public and declared as Code: void setnext(Dnode n) {link_next = n;} setprev() would be similar. __________________ dwk Seek and ye shall find. quaere et invenies.* "Simplicity does not precede complexity, but follows it." -- Alan Perlis "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra "The only real mistake is the one from which we learn nothing." -- John Powell Other boards: DaniWeb, TPS Unofficial Wiki FAQ: cpwiki.sf.net My website: http://dwks.theprogrammingsite.com/ Projects: codeform, xuni, atlantis, nort, etc.
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