Question

I am attempting to add a node to the end of a linked list. I use a void function and pass my struct into it, but once it has ran through the add function, my struct is still empty. here is the code.

struct part {
    char* name;
    float price;
    int quantity;
    struct part *next;
};

typedef struct part partType;

void addEnd(partType *item) {  
    partType *temp1=NULL, *temp2=NULL;
    char temp[100];  

    temp1 = (struct part *)malloc(sizeof(partType));  

    if (!temp1)
        printf("malloc failed\n");

    temp1->name = malloc(sizeof(char)*100);

    printf("Please enter item name: \n");
    fgets(temp, 100, stdin);     
    strcpy(temp1->name, temp);      

    printf("Please enter item price: \n");
    fgets(temp, 100, stdin);
    sscanf(temp, "%f", &temp1->price);      

    printf("Please enter item quantity: \n");
    fgets(temp, 100, stdin);
    sscanf(temp, "%d", &temp1->quantity);  

    // Copying the Head location into another node.  
    temp2 = item;  

    if (item == NULL) {  
        // If List is empty we create First Node.  
        item = temp1;  
        item->next = NULL;
        printf("%s%.2f\n%d\n", item->name, item->price, item->quantity);  
    } else {  
       // Traverse down to end of the list.  
       while (temp2->next != NULL)  
           temp2 = temp2->next;  

       // Append at the end of the list.  
       temp1->next = NULL;  
       temp2->next = temp1;
       printf("%s%.2f\n%d\n", item->name, item->price, item->quantity);
    }
} 

item is null when it is initially passed into the function, but for some reason comes out null even though i have the if statement that sets item equal to temp1.

Answer 1

You need to modify the value of the pointer, so you need an extra level of indirection:

void addEnd(partType **item)
{
   ...
   temp2 = *item;
   ...  
   if (*item == NULL)
   {
     *item = temp1;
     (*item)->next = NULL;
     printf("%s%.2f\n%d\n", (*item)->name, (*item)->price, (*item)->quantity);
     ...
}

and you would call this as

partType *newItem;
...
addEnd(&newItem);