what wrong with this function to add element to a linked list?

Question

Here is my code :

typedef struct node {
    int data;
    struct node *next;
} Node;

void add(Node *head, Node *node) {
    Node *ptr;
    ptr = head;
    if(head==NULL) {
        head=node;
    }
    else {
        while(ptr->next != NULL) {
            ptr = ptr->next;
        }
        ptr->next = node;
    }
}

Node* create(int a) {
    Node *node;
    node = (Node*)malloc(sizeof(Node));
    node->data = a;
    node->next = NULL;
    return node;
}

int main() {
    Node *head;
    head = NULL;
    int i;
    for(i=0; i<10; i++) {
        Node *node;
        node = create(i);
        add(head, node);
    }
}

Problem is : head is getting redefined in the function add, everytime add is called. why ?

Tom W · Accepted Answer · 2012-10-15 20:15:40Z

6

Because add is receiving a copy of your pointer when you call it. You set head in that function, but that changes the local copy, not other variable named head in main(). You would need to do something like this (I just put the lines to change; the rest look okay):

  void add(Node **head, Node *node) {
    *head = node;
  }



int main() {
    add(&head, node);
 }

answered Oct 15, 2012 at 20:15

Tom W

1,3348 silver badges9 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Yugal Jindle Over a year ago

Can I avoid using ** in some other way of implementing linkedlist ?

Yugal Jindle Over a year ago

I guess I can avoid using ** but not directly assigning to head but instead use pointers relative to head.

Tom W Over a year ago

@YugalJindle: In C, I'm not sure how to avoid passing in a pointer to your head pointer elegantly. In C++ you could use a reference. In C, the only other thing I can think of is to have your add function return the new head, then calls look like head = add(head, node);. But, that's probably worse.

Collectives™ on Stack Overflow

what wrong with this function to add element to a linked list?

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related