CODEWITHSUNDEEP
cmallocbinary-tree
viral_mutant
viral_mutant

Reputation: 1003

Issue with binary tree, C code, using malloc

I am trying to write a simple tree program in C, after a long long time :) but am stuck at the code where I add more nodes to my root node

Here is the code snippet:

  struct node* root;
  struct node* new_node;

  // Add a node
  new_node = malloc(sizeof(struct node*));
  new_node -> left = NULL;
  new_node -> data = 934;
  new_node -> right = NULL;

  // Mark this as root
  root = new_node;

  // Add a node
  new_node = malloc(sizeof(struct node*));
  new_node -> left = NULL;
  new_node -> data = 967;
  new_node -> right = NULL;

  // Make this left node of root
  root -> left = new_node;

  // Add a node
  new_node = malloc(sizeof(struct node*));
  new_node -> left = NULL;  // This line is the problem
  new_node -> data = 612;
  new_node -> right = NULL;

The line which is causing issue is marked with comment. The moment I make it NULL, the data 967 becomes 0.

However, if I put the new_node code in a function and call

root = new_node(934)
root -> left = new_node(967)
root -> right = new_node(612)

That works fine. I tried gdb on my code but could not understand why it would happen

Upvotes: 2

Views: 1721

Answers (1)

interjay
interjay

Reputation: 110108

new_node = malloc(sizeof(struct node*));

should be:

new_node = malloc(sizeof(struct node));

everywhere. Another possiblity is new_node = malloc(sizeof(*new_node));.

You need to allocate an entire node to point to, not just a pointer to a node.

Since you didn't allocate enough memory for a node, you got undefined behavior when writing to the fields of the node, which in your case caused it to overwrite existing data.

Upvotes: 1

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