Getting a segmentation fault trying to pass a node

Question

I'm new to C and I just started learning how to use pointers. I'm trying to create a function (r) that adds to a bst depending on if the parameter (int n) is greater than the root nodes value. However, I keep getting segmentation fault (core dumped) after running the following code. How do I fix it so that it can run normally without error.

struct node  {
    int data;
    struct node *left;
    struct node *right;
    }node;

struct node* newNode(int data){
    struct node* node = (struct node*)malloc(sizeof(struct node));
    node->data = data;
    node->left = NULL;
    node->right = NULL;
    return (node);
    }

void r (int n, struct node* root);

int main() {

    struct node *root = newNode(1);
    printf("%d", root->data);
    r(10, root);
    return 0;
    }

void r(int n, struct node* root){
    if(n > root->left->data){
       root->right = newNode(n);
       printf("New right is: %d\n", root->right->data);
    }
    else if(n < root->left->data){
       int a = root->left->data;
       root->left->data = n;
       root->right->data = a;
       printf("New left is: %d\n", root->left->data);

    }

       return;
    }

The very first time you call r(10, root) you have if (n > root->left->data).. In this case root->left is NULL. — lurker
– lurker, Commented Jun 21, 2019 at 23:09

Water · Accepted Answer · 2019-06-21 23:11:16Z

4

In the r function you wrote:

root->left->data

But root->left is equal to NULL. This will cause a segfault because you can't dereference a null pointer.

You can check for validity by doing something like:

// Make sure the left node exists, then do the test after
if (root->left && root->left->data > n)

since doing root->left will cause it to check that it's non-zero (meaning not NULL).

answered Jun 21, 2019 at 23:11

Water

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5 Comments

Cris Manrique Over a year ago

Oh wow, thanks I cant believe I didnt notice that. Thanks a lot.

Water Over a year ago

@CrisManrique Is there a way my answer could be improved? Or is it unacceptable in any way?

Cris Manrique Over a year ago

No, you were right, I had actually overlooked a simple mistake. You were right on the money. Sorry if I sounded sarcastic.

Water Over a year ago

@CrisManrique Is there any way I can make this answer better?

S.S. Anne Over a year ago

@CrisManrique If this answer helped you, please mark it as the accepted answer.

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