Creating Linked List using For Loop (c++)

Question

I was trying to create a linked list using a for loop but the 'new' in the for loop in the create() method didn't quite allocate a new slot to store new data. As a result, when I tried to print the list, I got an infinite loop. Can somebody tell me what's wrong here?

struct node
{
    double value;
    node * next_ptr;
    node(){}
    node(double val, node * p): value(val), next_ptr(p) {}
    ~node(){}

};

node * create()
{
    using namespace std;
    node temp = {0, nullptr};
    node * result;
    for(int i=1; i<5; ++i)
    {
        result = new node;
        result->value = i;
        result->next_ptr = &temp;
        temp = *result;
    }
    return result;
};

@WhozCraig: Thank you. You're right, the problem with my code was next_ptr kept pointing at one location (i.e., &temp). — Newbie
– Newbie, Commented Jul 16, 2015 at 0:49
~node(){} Advice -- Leave it empty. A node isn't supposed to be destroying anything. The list that manipulates the nodes should be responsible for removing/deleting the nodes. — PaulMcKenzie
– PaulMcKenzie, Commented Jul 16, 2015 at 1:13

sh03 · Accepted Answer · 2015-07-16 00:45:59Z

3

The reason you are probably getting an infinite loop is because in:

temp = *result;

you are copying the value of *result into a new object of type node, which is unrelated to the one you created.

What you want to do is store a pointer instead:

node* temp = nullptr;
node* result;
for(int i=0; i<5; ++i)
{
    result = new node;
    result->value = i;
    result->next_ptr = temp;
    temp = result;
}
return result;

Live demo

A part from the learning value, just stick to std::forward_list or std::list, for lists, instead. Or even better just use std::vector or other containers (depending on the use that you make of the container).

edited Jul 16, 2015 at 0:45

answered Jul 16, 2015 at 0:40

sh03

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Comments

learnnew · Accepted Answer · 2020-11-06 12:09:19Z

-1

a simple one to create linked in for loop

#include <iostream>
class LinkedList {
  public:
  int value;
  LinkedList * next;
};

int main()
{
  LinkedList *List = nullptr;
  LinkedList *head = List;
  LinkedList *prev;
  for (int i=0; i< 3;i++)
  {
    LinkedList *temp = new(LinkedList);

    temp->value = i;
    temp->next = nullptr;
    if (head == nullptr)
    {
      head = temp;
      prev = head;
    }
    else
    {
      prev->next = temp;
      prev = temp;
    }
  }

}

answered Nov 6, 2020 at 12:09

learnnew

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