Core dump with linked list

This is a discussion on Core dump with linked list within the C++ Programming forums, part of the General Programming Boards category; I'm writing a program that randomly creates a list of integers using a node class then splits the list at ...

  1. #1
    Registered User
    Join Date
    Jan 2005
    Posts
    46

    Core dump with linked list

    I'm writing a program that randomly creates a list of integers using a node class then splits the list at a certain value and sorts the resulting two lists then outputs them. right now I get no syntax errors, but I keep getting a segmentation fault. I bolded the statement I get a seg fault at.
    Code:
    NODE.H
    ----------
    //node class that holds int data and has accessor functions and a
    //constructor
    
    #include <cstdlib> //for NULL
    
    class node
    {
      public:
        node(int the_data = int(), node* link_field = NULL)
        {data = the_data; link = link_field;}
        void set_link(node* link_field) {link = link_field;}
        void set_data(int value) {data = value;}
        int get_data() {return data;}
        const int get_data() const {return data;}
        node* get_link() {return link;}
        const node* get_link() const {return link;}
      private:
        int data;
        node* link;
    };
    
    void head_insert (node*& head, node*& n1);
    void sort_list (node*& head);
    node* split_list(const int& value, node*& head);
    
    NODE.CC
    -----------
    #include <cstdlib>
    #include "node.h"
    
    using namespace std;
    
    void head_insert(node*& head, node*& n1)
    {
      n1->set_link(head);
      head = n1;
    }
    
    node* split_list(const int& value, node*& head)
    {
      node* head1, *head2, *temp;
    
      while (head != NULL)
      {
        temp = head;
        if (temp->get_data() < value)
        {
          head = head->get_link();
          head_insert(head2, temp);
        }else if (temp->get_data() >= value)
        {
          head = head->get_link();
          head_insert(head1, temp);
        }
      }
      head = head1;
      return head2;
    }
    
    void sort_list(node*& head)
    {
      int temp;
    
      for (node* ptr = head; ptr != NULL; ptr = ptr->get_link())
      {
        for (node* cursor = ptr; cursor != NULL; cursor = cursor->get_link())
        {
          if (cursor->get_data() > ptr->get_data())
          {
            temp = ptr->get_data();
            ptr->set_data(cursor->get_data());
            cursor->set_data(temp);
          }
        }
      }
    }
    
    MAIN.CC
    -----------
    #include <iostream>
    #include <cstdlib>
    #include "node.h"
    
    using namespace std;
    
    int main()
    {
      node* n1, *head, *head1, *temp;
      int value;
    
      srand(time(NULL));
    
      cout << "Please enter a value to split the list at: \n";
      cin >> value;
      
      n1 = new node;
      n1->set_data(rand()%25+1);
      head = n1;
    
      for (int i = 0; i < 10; i++)
      {
        n1->set_link(new node);
        n1 = n1->get_link();
        n1->set_data(rand()%25+1);
      }
      temp = head;
      //right here is where I get a segmentation fault. if I put a cout 
      //statement inside the loop it prints the values though....it's 
      //weird
      while (temp != NULL)
      {
        cout << temp->get_data();
        temp = temp->get_link();
      }
      head1 = split_list(value, head);
      sort_list(head1);
      sort_list(head);
      temp = head;
      cout << "Numbers over the split: ";
      while (temp != NULL)
      {
        cout << temp->get_data();
        temp = temp->get_link();
      }
      temp = head1;
      cout << endl << "Numbers under the split: ";
      while (temp != NULL)
      {
        cout << temp->get_data();
        temp = temp->get_link();
      }
      return 0;
    }
    please help

  2. #2
    Registered User
    Join Date
    Oct 2001
    Posts
    2,934
    > for (int i = 0; i < 10; i++)
    > {
    > n1->set_link(new node);
    > n1 = n1->get_link();
    > n1->set_data(rand()%25+1);
    > }
    You need to end the list here, by setting the last link to NULL.
    Code:
      for (int i = 0; i < 10; i++)
      {
        n1->set_link(new node);
        n1 = n1->get_link();
        n1->set_data(rand()%25+1);
      }
      n1->set_link(NULL);

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