How to add objects to singly linked list

Question

Information from the file is being read into the Car struct "newcar". I need to use the "sll_add" function below to add that information to the single liked list of type Carlist i named "list". I'm just having trouble understanding how it all starts. Thank you for any help.

int main (void)//main function
{ 

FILE *fp;//file pointer
fp = fopen("car_inventory.txt", "r");//opens the car inventory data within the program.
int num=0;//vairable created to keep track of the information.
int year;//, choice;//variables use for user input.
char str1[100];//string created to ensure the program reads the information from the original file correctly. 
Carlist list;//creates a string of type "Car" named file to hold up to 100 cars. 
Car newcar;//Car variable to store the info from the file. 

list *last=num;

if (fp)
    {
        {                   
        while(!feof(fp))//takes input from the data file.
            {
        fgets(str1,50, fp);
        sscanf(str1,"%d %s %[^\n]s", &newcar.year, newcar.make, newcar.model);

        fgets(str1,50, fp);
        sscanf(str1,"%[^\n]s", newcar.style);

        fgets(str1,50, fp);
        sscanf(str1,"%[^\n]s", newcar.color);

        fgets(str1,50, fp);
        sscanf(str1,"%s", newcar.mileage);

        fgets(str1,50, fp);
        sscanf(str1,"%c", &newcar.air_condition);

        fgets(str1,50, fp);
        sscanf(str1,"%s", newcar.inventory_num);

        fgets(str1,50, fp);
        sscanf(str1,"%lf", &(newcar).price);

        fgets(str1,50, fp);
        sscanf(str1,"%[^\n]s", newcar.previous_owner);

        fgets(str1,50,fp);


        num++;
        sll_add(*newcar, &list);
            }
        }

return 0;


#define MAX_CARS     100

/* Type definitions */

typedef struct car
{
    int year;
    char make[25];
    char model[25];
    char style[25];
    char color[20];
    char mileage[8];
    char air_condition;
    char inventory_num[16];
    double price;
    char previous_owner[30];
    struct car *next;

} Car;


typedef struct carlist
{
    Car *first;
    Car *last;
} Carlist;


void sll_init(Carlist *l);
Car *sll_first(Carlist *l);
Car *sll_end(Carlist *l);
Car *sll_next(Car *current, Carlist *l);
Car *sll_retrieve(Car *element, Carlist *l);
void sll_delete(Car *c, Carlist *l);
void sll_delete_year(Carlist *l, int year);
void sll_add(Car *newcar, Carlist *l);


    #endif

Carey Gregory · Accepted Answer · 2013-09-24 20:05:44Z

Start from the beginning. First, your Carlist needs to be initialized, so you need to flesh out the sll_init() function. This one is very easy since all it needs to do is set the first and last pointers to null. It might look something like this:

void sll_init(Carlist *l)
{
    l->first = l->last = NULL;
}

Next, you need to be able to add entries to your list, so you need to flesh out sll_add(). It might look something like this:

void sll_add(Car *newcar, Carlist *l)
{
    Car *new = malloc(sizeof(*new));
    *new = *newcar;
    new->next = NULL;    // just to be safe in case newcar wasn't properly initialized

    if (l->first == NULL)
    {
        // the list is empty, so add the first entry
        l->first = l->last = new;
    }
    else
    {
        // the list is not empty, so append a new entry to the end
        l->last->next = new;
        l->last = new;
    }
}

With this, you should be able to get started.

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