Thread: Cannot make linked lists work

Hi! I am trying to create a simple program to create a linked list and delete one of the nodes. When I run my program the print out for the "old list" is 4 and the "new list" is nothing. I am not sure if my problem is in the way I print the lists or in the way I make them or both. From some examples I have found on the web I suspect the problem is in how I print the lists, but I don't know for sure. My code is below:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct myllist
{
        int info;
        struct myllist * link;
} myllist;

void GetNewNode (int newInfo, myllist * pNode);
void disposeOfNode(myllist *change, myllist *remove);

main(){
       //setup nodes
       myllist * pNode;
       pNode = (myllist *) malloc(sizeof(*pNode));
       GetNewNode(4, pNode);
       
       myllist * pNode2;
       pNode2 = (myllist *) malloc(sizeof(*pNode));
       GetNewNode(5, pNode2);
       
       myllist * pNode3;
       pNode3 = (myllist *) malloc(sizeof(*pNode));
       GetNewNode(6, pNode3);
       
       //print values to check
       printf("%d\n%d\n%d\n", pNode->info, pNode2->info, pNode3->info);
       
       //link nodes together
       pNode->link = pNode2;
       
       //print list
       printf("Old List:\n");
       myllist * tmp;
       tmp = pNode;
       while(tmp->link != NULL){
                       printf("%d", tmp->info);
                       tmp = tmp->link;
                       }
       
       //get rid of pNode2
       disposeOfNode(pNode, pNode2);
       
       //print new list
       printf("\nNew List:\n");
       tmp = pNode;
       while(tmp->link != NULL){
                       printf("%d", tmp->info);
                       tmp = tmp->link;
                       }
       
       //end
       getchar();
}

void disposeOfNode(myllist *change, myllist *remove){
     change->link = remove->link;
     free(remove);
     return;
     }

void GetNewNode (int newInfo, myllist * pNode){
      /*myllist * pNode;
      pNode = (myllist *) malloc(sizeof(*pNode));*/
      if(pNode == NULL){
               printf("error: malloc failed");
               }else{
                     pNode->info = newInfo;
                     pNode->link = NULL;
                     }
      return;
}

Could someone tell me what I did wrong? I have been trying to figure this out for weeks without luck. Thanks!

Code:

     while(tmp->link != NULL){
                       printf("%d", tmp->info);
                       tmp = tmp->link;
                       }

This will never print out the last entry in the list. You should check whether tmp itself is NULL instead.

This code is pure C (my clue was that your main() doesn't return int explicitly). A moderator should move this to the C forum.

Originally Posted by tabstop

Code:

     while(tmp->link != NULL){
                       printf("%d", tmp->info);
                       tmp = tmp->link;
                       }

This will never print out the last entry in the list. You should check whether tmp itself is NULL instead.

Thank you, I fixed that and now my program works.