Issue with linking new node to Linked lists in c

Question

I'm new to C and new to programming as well and I've just started looking at linked lists.

static struct post {
    char * str;
    struct post * next;
}
head = {0, NULL};


int stringdb_add(const char * str) {
    int pos = 0;
    struct post * new_input = (struct post * ) malloc(sizeof(struct post));
    new_input - > str = (char * ) malloc(strlen(str) + 1);

    if (head.next == NULL) {
        strcpy(new_input - > str, str);
        new_input - > next = NULL;
        head.next = new_input;
    } else {
        while (head.next - > next) {
            ++pos;
            head.next = head.next - > next;
        }
        strcpy(new_input - > str, str);
        new_input - > next = NULL;
        head.next - > next = new_input;
    }

    return pos;
}

The function "stringdb_add" is supposed to return the position the new node has been placed in, but when I test the function I only get (00111111....).

This is probably because the list never links properly.

You get a +1 for trying .. But might get a -1 for indentation - sort it — Ed Heal
– Ed Heal, Commented Jan 25, 2014 at 9:39

cnicutar · Accepted Answer · 2014-01-25 09:34:34Z

3

while (head.next->next) {
   ++pos;
   head.next = head.next->next;        
}

You are permanently changing head.next which is surely not what you want. You probably want something like:

struct post *p = &head;
while (p->next->next)
/* ... */

Nitpick: strcpy(new_input->str, str) can be in a single place, before the if.

answered Jan 25, 2014 at 9:34

cnicutar

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1 Comment

Adlon Over a year ago

Okay, i totaly got it working now, the whole p pointer made everything easier. thanks for your help and a really qucik answer! :)

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