GDB error I don't recognize: “Program received signal EXC_BAD_ACCESS”

Question

My code handles Binary Search Trees, so those are the structures I a referencing in the code. But gdb seems to crash before running through any of my code.

/* my own recursive function, counts number of nodes in tree */
int count_nodes(bst_node_t *node)
{
  if( node == NULL )
    return 0;
  /* if this is a leaf, return 1 */
  if( node->left == NULL && node->right == NULL )
    return 1;
  /* if left side empty, return 1 + count for right subtree */ 
  else if( node->left == NULL )
    return 1 + count_nodes(node->right);
  /* if right side empty, return 1 + count for left subtree */
  else if( node->right == NULL )
    return 1 + count_nodes(node->left);
  /* otherwise, return 1 + count for both left and right subtrees */ 
  else
    return 1 + count_nodes(node->left) + count_nodes(node->right);
}

/* mallocs the header for the BST, initializes it, and returns pointer to it */
bst_t *bst_create (void)
{
  bst_t *tree = (bst_t *)malloc(sizeof(bst_t));
  tree->root = NULL;
  tree->tree_size = 0;
  tree->num_recent_key_comparisons = 0;
}

int main(void) 
{
  bst_t *tree = bst_create();
  printf("size = %d, comparisons = %d\n", tree->tree_size, tree->num_recent_key_comparisons);
  printf("size from count_nodes = %d\n", count_nodes(tree->root));
  free(tree);
}

Running this in gdb gets me the following crash:

Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0x000000000000000c
0x0000000100000cc8 in main ()

If I just run the code, it gets through the first print statement in main(), but crashes on the call to count_nodes, so I thought it was some odd pointer error, but gdb didn't point out any line in the code, it gave e that error without printing anything out, which makes me think it didn't get far in the code.

ps I only JUST installed gdb and MAKE on my mac, got it with the Xcode downloads from apple's developer website. So there may have been some error with how I installed it.

Answer 1

You're not returning tree from bst_create() . Your program causes undefined behaviour - anything could happen. You should turn some warnings on.

Editorial aside: Don't cast the return value of malloc() in a C program.

Answer 2

bst_t *bst_create (void)
{
  bst_t *tree = (bst_t *)malloc(sizeof(bst_t));
  tree->root = NULL;
  tree->tree_size = 0;
  tree->num_recent_key_comparisons = 0;
}

would work better with a

return tree;

Answer 3

You forgot to return the node in your bst_create

bst_t *bst_create (void)
{
  bst_t *tree = (bst_t *)malloc(sizeof(bst_t));
  tree->root = NULL;
  tree->tree_size = 0;
  tree->num_recent_key_comparisons = 0;
  return tree;
}