Cannot make linked lists work

This is a discussion on Cannot make linked lists work within the C++ Programming forums, part of the General Programming Boards category; Hi! I am trying to create a simple program to create a linked list and delete one of the nodes. ...

  1. #1
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    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!

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    14,185
    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.

  3. #3
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    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.

  4. #4
    C++まいる!Cをこわせ! Elysia's Avatar
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    Posts
    22,543
    Indeed, and how about typedef struct, free, malloc and printf?
    C. All C! And C99 too, it looks like, if this compiles.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  5. #5
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    Quote Originally Posted by tabstop View Post
    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.

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