Thread: Binary Search Tree

Can anyone see why the delete function is returning a segmentation fault in this code??
the values "d", "b", "f", "a", "c", "e", "g" are being insterted and printed correctly from a seperate source file. as soon as i try to delete a node i cant print or do anything.
thanks

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "bst.h"
#include "mylib.h"

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

bst bst_new(){
   return NULL;
}

bst bst_insert(bst b, char *key){
   if (b == NULL) {
      b =  emalloc(sizeof *b);
      b -> key = key;
      b -> left = NULL;
      b -> right = NULL;
   } else if (strcmp(key, b -> key) < 1) {
      b -> left = bst_insert(b -> left, key);
   } else {
      b -> right = bst_insert(b -> right, key);
   }
   return b;
}

char *bst_search(bst b, char *key){
   if (b == NULL) {
      return NULL;
   } else if (b -> key == key) {
      return b -> key;
   } else if (strcmp(key, b -> key) > 0) {
      return bst_search(b -> left, key);
   } else {
      return bst_search(b -> right, key);
   }
}

void bst_inorder(bst b, void f(char *s)){
   if (b == NULL) {
      return;
   } else {
      bst_inorder(b -> left, f);
      f(b -> key);
      bst_inorder(b -> right, f);
   }
}

void bst_preorder(bst b, void f(char *s)){
   if (b == NULL) {
      return;
   } else {
      f(b -> key);
      bst_preorder(b -> left, f);
      bst_preorder(b -> right, f);
   }
}

bst bst_delete(bst b, char *key){
   int x = strcmp(key, b->key);
   printf("%d\n", x);

   if (x<0) {
      return bst_delete(b->left, key);
   } else if (x > 0) {
      return bst_delete(b->right, key);
   } else {
      if (b->left == NULL && b->right == NULL) {
         b->key = NULL;
         b->left = NULL;
         b->right = NULL;
         return b;
      } else if (b->left == NULL) {
         b->key = b->right->key;
         b->right = b->right->right;
         b->left = b->right->left;
         return b;
      } else if (b->right == NULL) {
         b->key = b->left->key;
         b->right = b->left->right;
         b->left = b->left->left;
         return b;
      } else {
         bst b2 = b->right;
         while (b2->left != NULL) {
            b2=b2->left;
         }
         b->key = b2->key;
         return bst_delete(b2, b2->key);
      }
   }
}