c++ - Doubly linked list Core dump -

thanks in advance.

i making doubly linked list.

everything working fine, realized when added new class node somewhere in middle, left pointer still pointing @ node before (now 2 spaces away).

so added new node pointer on line 46.

then on line 51 told node point new node.

so :

• first had new node temp off in space

• then make pointer temp2 loop through list

• lastly tell temp3 point node after temp2's node

after function runs, order should temp2->temp->temp3

my main point: after added line 51, program core dumps(segmentation fault) , closes out.

how can fix this? happens when add isn't taking place of head pointer.

void add(node *&head, node *&tail, node *&current) {     node *temp = new node;  //creates pointer pointing new class node     cin >> temp->letter;    // user input      current = head; // creates pointer point @ first node     while (current != null) // while list isn't empty     {         if (current->letter == temp->letter)         { // letter exists             cout << "duplicate: " << temp->letter << endl << endl;             return;         }         else         { // loop through list moving tail pointer end while checking duplicates             tail = current;             current = current->right_link;         }     }      current = temp; // current = new added node      if (isempty(head))     { // if first node         temp->left_link = null;         temp->right_link = null;         head = temp; // head ,          tail = temp; // tail both point first , node.     }     else     { // if new letter value less head value         if(temp->letter < head->letter)         {             temp->right_link = head; // node points (right) head             temp->left_link = null; // left node point nothing.             head->left_link = temp; // head (currently second node) points (left) first node             head = temp; // head pointer moves first position         }         else         { // if new node goes anywhere other head             node *temp2 = head; // new node cycle through list             while(temp2->right_link != null && temp2->right_link->letter < temp->letter)             { // if temp2 points node , node's value less temp node value                 temp2 = temp2->right_link;             }             node *temp3 = temp2->right_link;             temp->right_link = temp2->right_link; // when temp2 stops looping, temp point                                                   // same node temp2.             temp2->right_link = temp; // temp2's current node point temp, causing temp                                 // added list (after temp2)             temp3->left_link = temp; // point node (after newly inserted node) left new node             temp->left_link = temp2; // connects left pointer between temp , temp2             if(temp->right_link == null)                 tail = temp;         }     }     cout << "added : " << temp->letter << endl << endl; } 

if temp2->right_link == null

 46      node *temp3 = temp2->right_link; 

is null pointer, can't

 51      temp3->left_link = temp; 

which should have been obvious if used debugger.