Question

I’m trying to create a singly linked list from an input text file for an assignment. I’m trying to do it a little bit at a time so I know my code is not complete. I tried creating the head pointer and just printing out its value and I can’t even get that to work, but I’m not sure why. I included the struct, my create list, and print list functions. I didn’t include the open file since that part works.

typedef struct List
{
   struct List *next;   /* pointer to the next list node */
   char *str;           /* pointer to the string represented */
   int count;           /* # of occurrences of this string */
} LIST;

LIST *CreateList(FILE *fp) 
{
    char input[LINE_LEN];
    LIST *root;             /* contains root of list             */
    size_t strSize;         
    LIST *newList;          /* used to allocate new list members */

    while (fscanf(fp, BUFFMT"s", input) != EOF) {

        strSize = strlen(input) + 1;

        /* create root node if no current root node */
        if (root == NULL) {
            if ((newList = (LIST *)malloc(sizeof(LIST))) == NULL) {
                printf("Out of memory...");
                exit(EXIT_FAILURE);
            } 
            if ((char *)malloc(sizeof(strSize)) == NULL) {
                printf("Not enough memory for %s", input);
                exit(EXIT_FAILURE);
            }
                memcpy(newList->str, input, strSize);   /*copy string    */
                newList->count = START_COUNT;
                newList->next = NULL;
                root = newList;
        }
    }
        return root;
}

/* Prints sinly linked list and returns head pointer */
LIST *PrintList(const LIST *head) 
{
    int count;

    for (count = 1; head != NULL; head = head->next, head++) {
        printf("%s    %d", head->str, head->count);
    }                       
    return head;     /* does this actually return the start of head ptr, b/c I want to 
                            return the start of the head ptr. */
}

Answer 1

root has an undefined value, so it won’t initialize. The second line of CreateList should be

LIST *root = NULL;

Also, further down there is allocation apparently for the details of the item, but a) the code fails to capture the allocation and save it anywhere, and b) the size of the allocation should be strSize, not the length of the variable itself. There are several ways to fix it, but the most straightforward would be:

newList->str = (char *)malloc(strSize);
if (newList->str == NULL)