我想问问怎么FREE 一个BST......谢谢..下面是我写的.大家看看对不.有没有别的写法

struct bstnode {
     char *key;
     bst left;
     bst right;
};

bst bst_new() {
     bst b = NULL;
     return b;
}

bst bst_insert(bst b, char *key) {
     if(b == NULL){
     b = emalloc(sizeof *b);
     b->key = emalloc((strlen(key)+1) * sizeof b->key[0]);
     strcpy(b->key,key);
} else if (strcmp(b->key,key)>0){
    b->left = bst_insert(b->left,key);
} else if (strcmp(b->key,key)<0){
    b->right = bst_insert(b->right,key);
}
return b;
}
....
....
....
....
bst bst_destroy(bst b){
   if ( b == NULL) return;
   bst_destroy(b->left);
   bst_destroy(b->right);
   free(b->key);
   free(b);
   b = NULL;
   return b;
}

謝謝...大家幫幫我啊..