algorithm - C - freeing memory of a binary tree using post-order traversal -

i want remove binary tree using post-order traversal. meaning left part of tree should removed first right 1 then remove whole tree , free memory in second function follows after. i'm not allowed changed arguments of function , can play inside of it:

#include <stdio.h> #include <stdlib.h> #include <string.h> #include "telefonbuch.h"  static inline bstree * create_node(unsigned long phone, char * name) {   bstree * newnode = (bstree *) malloc(sizeof(bstree));    newnode->key.phone = phone;   strcpy(newnode->key.name, name);   newnode->left = null;   newnode->right = null;    return newnode; }  void bst_insert_node(bstree * bst, unsigned long phone, char * name) {     if (bst == null)     {         return;     }      if (bst->key.phone > phone)     {         if (bst->left == null)         {             bst->left = create_node(phone, name);             return;         }          bst_insert_node(bst->left, phone, name);     }     else     {         if (bst->right == null)         {             bst->right = create_node(phone, name);             return;         }          bst_insert_node(bst->right, phone, name);      } }  bst_node * find_node(bstree* bst, unsigned long phone) {   if (bst == null)   {       return null;   }    if(bst->key.phone > phone)   {       return find_node(bst->left, phone);   }   else if (bst->key.phone < phone)   {       return find_node(bst->right, phone);   }    return &(bst->key); }  void bst_in_order_walk_node(bst_node* node) { }  void bst_in_order_walk(bstree* bst) {    int temp = 0;    int level;     while(temp < level)    {        printf("-");        ++temp;    }     printf(" (%ld-%s)\n", bst->key.phone, bst->key.name);     if (bst->left != null)    {       print_tree(bst->left, level + 1);    }     if (bst->right != null)    {       print_tree(bst->right, level + 1);    } }  void bst_free_subtree(bst_node* node) {      …what goes here?…  }  void bst_free_tree(bstree* bst) {   if(bst==null)       return;   bst_free_tree(bst->left);   printf("deleting %d node.\n",bst->key);   free(bst);   bst_free_tree(bst->right); }   

here structure definitions:

typedef struct _bst_node {   char name[60];   unsigned long phone; } bst_node;  typedef struct _bstree {   bst_node key;   struct _bstree * left;   struct _bstree * right;   } bstree; 

could me finish/correct code?

you have:

void bst_free_tree(bstree* bst) {   if(bst==null)       return;   bst_free_tree(bst->left);   printf("deleting %d node.\n",bst->key);   free(bst);   bst_free_tree(bst->right); } 

this deletes current node 'in-order', , accesses freed memory after freeing it. not good!

you need close relation:

void bst_free_tree(bstree* bst) {     if (bst == null)         return;     bst_free_tree(bst->left);     bst_free_tree(bst->right);     printf("deleting %d node.\n", bst->key);     free(bst); }   

this traverses , releases left sub-tree, right sub-tree, , releases current node.

i don't see need bst_free_subtree() function; bst_free_tree() function frees sub-trees equally well.