Thread: Help figuring out Linked List insertion

I'm trying to figure out how to insert a node into a linked list at a particular location based on a time and am confused. Any suggestions or help would be appreciated.

I have this declared outside of everything globally.

Code:

struct aTime {    
    char        name[LENGTH];
    int        time;
    struct aTime* next;
};


struct aTime* head = NULL;

And then this function that is used to add nodes (aTime structs) to a linked list. It adds the first node fine, but not subsequent ones. I think this is because I have while p-> != NULL but it is always going to be null when the function is called since I create a new aTime struct. So I guess my question is how, after one struct has been added at the beginning, do I point to the head node and traverse the list, insert a node, and make sure everything is still linked? Do I need another temp aTime struct?

Code:

void add_time(char name[LENGTH], int seconds)
{
    struct aTime *p;
    p = (struct aTime *) malloc(sizeof(struct aTime));


    if (head == NULL)
    {    
        strcpy(p->name, name);
        p->seconds = seconds;
        p->next = list_head;
        list_head = p;
        return;
    }
    else
    {
        while (p->next != NULL)
        {
            if (p->seconds < seconds)
            {
                strcpy(p->name, name);
                p->seconds = seconds;


                return;
            }
            else
            {
                p = p->next;
            }
        }
    }
}

Thanks for any help or suggestions.

After the else, p->next is used but never initialized, and it's not yet part of the linked list. You need to use a temp pointer to atime, initialize it temp = head, and advance that temp pointer to the insertion spot.

Originally Posted by rcgldr

After the else, p->next is used but never initialized, and it's not yet part of the linked list. You need to use a temp pointer to atime, initialize it temp = head, and advance that temp pointer to the insertion spot.

Thanks for the suggestions.

So if I make a

Code:

struct aTime *temp = list_head;

Do I just need to use that instead of p after the else? Since it is pointing at the head of the linked list and then traverses through it?

Hrm..I found a few examples online that don't really look much like what I have so I guess I'll keep working at it.

First initialize a temp and temp1 pointer which is equal to head pointer just before while loop

Code:

 temp=head;

Code:

while(temp->next != NULL)
{
  temp1=temp;
  temp=temp->next;
}
if(p->secounds < secounds)
{
  p->next=temp;
  temp1->next=p;
}
else
{
  temp->next=p;
}