c++ - This code looks like it deletes this object but it doesnt? -

the following code removing node of binary tree. have stepped through code , i'm pretty sure problem lies in last "else if" in destroy(). i'm trying replace given node smallest node delete given node. remove() , findsmallest work should think. when reprint tree no changes have been made.i'm beginner, hints/help appreciated!

void remove(key k)  {     remove(k, root); } void remove(key k, binarysearchtreenode<key, value> * n) {     if (n)     {         if (root->key == k)             removeroot();         else         {             //1 child             if ( (n->left != nullptr) && (k < n->key) )             {                 if (k == n->left->key)                     destroy(n->left, true);                 else                     remove(k, n->left);             }             else if (n->right && k > n->key )             {                 if (k == n->right->key)                     destroy(n->right, false);                 else                     remove(k, n->right);             }             else             {                 cout << "no remove\n";             }         }     }     else         cout << "trww empty"; }  void destroy(binarysearchtreenode<key, value> * n, bool isleft) {     if (n == nullptr)     {         return;     }     else if (!n->left && !n->right)     {         n->left = nullptr;         n->right = nullptr;         n->parent = nullptr;         delete n;         n = nullptr;     }     else if (!n->left && n->right)     {         isleft ? n->parent->left = n->right : n->parent->right = n->right;         cout << "killing " << n->key << endl;         n->parent = nullptr;         n->left = nullptr;         n->right = nullptr;         delete n;         n = nullptr;     }     else if (n->left && !n->right)     {         isleft ? n->parent->left = n->left : n->parent->right = n->left;         cout << "killing " << n->key << endl;         n->parent = nullptr;         n->left = nullptr;         n->right = nullptr;         delete n;         n = nullptr;     } /* program goes code below*/     else if (n->left && n->right)     {         binarysearchtreenode<key, value> * small = findsmallest(n->right);         if (isleft)             n->parent->left  = small;         else             n->parent->right = small;          small->parent = n->parent;         small->left = n->left;         small->right = n->right;         n->parent = nullptr;          n->left = nullptr;         n->right = nullptr;         //key smallkey = small->key;         //value smallvalue = small->value;         cout << "killing " << n->key << endl;         delete n;         n = nullptr;      }     else         cout << "fail";   }  binarysearchtreenode<key, value> * findsmallest(binarysearchtreenode<key, value> * n) {     if (!n)         return part;     else      {         if (n->left)             return findsmallest(n->left);         else             return n;     }  } 

you give node destroy() pointer. means can things did, except change variable in calling method.

when n= nullptr; in destroy() changes local variable. doesn't change calling variable, example n->right nullptr still point place deleted object was.

if set parameter reference pointer (*&) can change calling variable , remove pointer node.

the reason why looks original tree because memory allocated deleted node happened not reused yet. later , tree cause access wrong pointer , maybe crash. behaviour undefined.