linked list print/delete function bombs program - c++

Question

I realize this might be a simple problem but I'm not catching it. My requirement is that I have to "4) Delete the linked list and print the list out again. (making sure its gone from memory)"
So I call the delete function and stepping through it, head should be set to NULL when the function finishes.
/*----------------------------------------------------------------------------
* Function: deleteList
* Purpose: delete a link list
* Arguments: head - a pointer to the first node in the linked list
* Returns: N/A
------------------------------------------------------------------------------*/
void deleteList(node *head)
{
struct node *temp;
// Loop through the list, deleting one node at a time.
while(head != NULL)
{
temp = head->next;
delete(head);
head = temp;
}
}
So when I call the print function and send in head, it should be NULL and catch on the first if statement and return to main. But it is bombing out instead.
/*----------------------------------------------------------------------------
* Function: printList
* Purpose: prints a link list
* Arguments: head - a pointer to the first node in the linked list
* Returns: N/A
------------------------------------------------------------------------------*/
void printList(node *head)
{
if (head == NULL)
{
cout << "Empty List!\n";
return;
}
struct node *temp;
temp = head;
// Loop through the list, printing one node at a time.
while(temp->next != NULL)
{
cout << temp->next->element << endl;
temp = temp->next;
}
}
Now if I use the following in main it works fine. But I'd like to know what small thing im missing in the print function. Been banging my head on this for a while now so I'd thought I would step back and ask for a little guidance.
int main()
{
....
cout << "\n***************** DELETE LIST & PRINT ********************\n";
deleteList(head);
cout << head->element << endl; // This works and shows the list is empty.
//printList(head); // This bombs the program.
....
}
Thanks much.
Node is defined below:
struct node
{
string element;
struct node *next;
};
Declaring head in main:
struct node *head;
//creating head node.
if ((head=new(node)) == NULL)
{
cout << "Error: Could not create head node.\n";
return 1;
}
head->next = NULL;

Answer 1

When you use in main
deleteList(head);
A copy of the pointer "head", pointing to the same place, is passed as parameter.
So, if you change the variable that "head" points to, e.g.:
delete(head);
this will be visible in main(). But when you update the pointer "head" itself, e.g.:
head = temp;
The only pointer updated is the one in the scope of the function, and not the one in main. So now your "head" pointer in main points to a deleted variable.
To solve the issue, you could return the new place that "head" should point to, like so:
node *deleteList(node *head)
{
struct node *temp;
// Loop through the list, deleting one node at a time.
while(head != NULL)
{
temp = head->next;
delete(head);
head = temp;
}
return head;
}
And call it with
head = deleteList(head);