Why is this function showing segmentation fault?

Question

This is a function to insert into a sorted linked list but it is showing segmentation fault (SIGSEGV)

void sortedInsert(struct node **head_ref, int data) {
    struct node *new_node, *prev, *current;
    new_node = (struct node*)malloc(sizeof(struct node));
    new_node->data = data;
    new_node->next = NULL;
    if (*head_ref == NULL || (*head_ref)->data > data) {
        new_node->next = *head_ref;
        *head_ref = new_node;
        return;
    }
    current = *head_ref;
    prev = NULL;
    while (current->data < data && current != NULL) {
        prev = current;
        current = current->next;
    }
    prev->next = new_node;
    new_node->next = current;
}

Most likely because it has one or more bugs, which you can find using a debugger. — juanchopanza
– juanchopanza, Commented Aug 28, 2017 at 17:32
while(current->data<data&&current!=NULL) should be while(current!=NULL && current->data < data) — BLUEPIXY
– BLUEPIXY, Commented Aug 28, 2017 at 17:36
this is a run time question, but the posted code does not compile. Please post a minimal reproducible example — user3629249
– user3629249, Commented Aug 29, 2017 at 5:16

Ankur Agrawal · Accepted Answer · 2017-08-28 17:40:27Z

3

Most likely the segmentation fault here is because of the statement:

while(current->data<data&&current!=NULL)
    {
        prev=current;
        current=current->next;
    }

The current pointer here is being dereferenced without being checked for NULL. You should try changing the condition to while(current && current->data<data) so that the pointer gets checked for NULL before being dereferenced.

answered Aug 28, 2017 at 17:40

Ankur Agrawal

482 silver badges5 bronze badges

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

Comments

chqrlie · Accepted Answer · 2017-08-29 05:31:48Z

1

The bug is here: while (current->data < data && current != NULL). The pointer must be checked against NULL before it is dereferenced:

while (current != NULL && current->data < data)

Note that this function can be simplified with a single loop:

void sortedInsert(struct node **head_ref, int data) {
    struct node *new_node;
    while (*head_ref && (*head_ref)->data <= data) {
        head_ref = &(*head_ref)->next;
    }
    new_node = malloc(sizeof(struct node));
    if (new_node == NULL) {
        /* handle the error */
        ...
    } else {
        new_node->data = data;
        new_node->next = *head_ref;
        *head_ref = new_node;
    }
}

answered Aug 29, 2017 at 5:31

chqrlie

152k12 gold badges145 silver badges231 bronze badges

Comments

user3629249 · Accepted Answer · 2017-08-29 05:21:09Z

0

if this statement fails on the first iteration:

while(current->data<data&&current!=NULL)

then this statement:

prev->next=new_node;

will be accessing an offset from address 0 which will almost always result in a seg fault event.

answered Aug 29, 2017 at 5:21

user3629249

16.6k1 gold badge18 silver badges17 bronze badges

Collectives™ on Stack Overflow

Why is this function showing segmentation fault?

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related