Hi I've been trying to code a bst based upon this link below:

I've adopted a similar strategy, whilst making some modifications, however for me I'm having a problem in that every time I go to add a new node to the bst, the root is always null, and thus no to *bst occur once the insert function has terminated.

I think I could use a pointer to a pointer to fix this, but what I don't understand is how the code in the above link works, when mine is basically the same.

Here's my code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct node{
	struct node *left, *right;
	char *data;
	int count;

struct bst{
	struct node *root;

bst *bst_create( ){
	struct bst *bstTree;

	if ((bstTree = (struct bst *)malloc(sizeof(struct bst))) != NULL) {
		bstTree->root = NULL;
		return bstTree;


node *create_node(char *data){
	struct node *tempNode;

	if ((tempNode = (struct node *)malloc(sizeof(struct node))) != NULL) {
		tempNode->data = data;
		tempNode->left = NULL;
		tempNode->right = NULL;
		tempNode->count = 0;
		return tempNode;

int bst_insert(bst *bstTree, char *data){

	struct bst *tempBst = bstTree;
	struct tldnode *current = bstTree->root;

	struct tldnode *newNode = create_node(data);

	if ( current == NULL){
		current = newNode;
		return 1;	
	for ( ; ;){

		cmp = strcmp(data,current->data);

		if (cmp == 0){
			return 1;

		if (cmp < 0)
			current = current->left;

			current = current->right;

		if (current == NULL)

	if (cmp < 0)
		current->left = newNode;
		current->right = newNode;

	return 1;


Edited by axa121: n/a

5 Years
Discussion Span
Last Post by axa121

Also heres the insert function for the above link:

void **
bst_probe (struct bst_table *tree, void *item)
  struct bst_node *p, *q; /* Current node in search and its parent. */
  int dir;                /* Side of |q| on which |p| is located. */
  struct bst_node *n;     /* Newly inserted node. */

  assert (tree != NULL && item != NULL);

  for (q = NULL, p = tree->bst_root; p != NULL; q = p, p = p->bst_link[dir])
      int cmp = tree->bst_compare (item, p->bst_data, tree->bst_param);
      if (cmp == 0)
        return &p->bst_data;
      dir = cmp > 0;

  n = tree->bst_alloc->libavl_malloc (tree->bst_alloc, sizeof *p);
  if (n == NULL)
    return NULL;

  n->bst_link[0] = n->bst_link[1] = NULL;
  n->bst_data = item;
  if (q != NULL)
    q->bst_link[dir] = n;
    tree->bst_root = n;

  return &n->bst_data;
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