Link List null ptr error - c++

Question

This is in the main function. Using visual studio 2017.
list a;
a.insertAtEnd("i", 1);
a.insertAtEnd("love", 1);
Here in the main when second insert at end is called. The program crashes and says the getnext() is NULL. Even though at the creation of every new node the next pointer is declared NULL.
class node {
public:
node(string value) {
next = NULL;
data = value;
}
void setNext(node *temp) {
next = temp;
}
void setdata(string value) {
data = value;
}
node* getNext() {
return next;
}
Debugger shows this function to be at fault^
string getData() {
return data;
}
void createDetail() {
detail *tmp = new detail();
d = tmp;
}
void setDetail(int lin) {
d->insertAtEnd(lin);
}
void getDetails() {
d->print();
}
private:
node *next;
string data;
detail *d;
};
class list {
public:
list() {
head = NULL;
}
void insertAtEnd(string, int);
void insertAfter(string, string);
void display();
private:
node *head;
};
void list::insertAtEnd(string value, int lin) { //main func being used
if (head == NULL) {
node *temp = new node(value);
temp->createDetail();
temp->setDetail(lin);
head = temp;
}
else {
node *temp2 = head;
while (temp2->getNext() != NULL || temp2->getData()!=value)
{
temp2 = temp2->getNext();
}
if (temp2->getData() == value)
{
temp2->setDetail(lin); //if same line then increment frequency, dont create new detail as word exists
}
else
{
node *temp = new node(value);
temp->createDetail();
temp->setDetail(lin);
temp2->setNext(temp);
}
}
}

Answer 1

In
while (temp2->getNext() != NULL || temp2->getData() != value)
{
temp2 = temp2->getNext();
}
temp2->getNext() != NULL will be be NULL for the last item in the list, and the data in the last item in the list may not match value. In this case,
while (NULL != NULL || "I" != "love") // false or true = true. Enter loop
{
temp2 = NULL;
}
Next iteration fails because
while (NULL->getNext() != NULL || temp2->getData() != value)
{
temp2 = temp2->getNext();
}
Ka-blam.
My solution changes a lot of code. You might not like it. Also note I've removed everything that will not compile because it was left out of the question.
class node
{
friend class list; // list has access to node's private members
public:
node(string value)
{
next = NULL;
data = value;
}
// removed setNext. Only list should ever be allowed to set the next member
void setdata(string value) {
data = value;
}
// same deal for get. Some shmuck could delete link->getNext();, so why let them?
string getData()
{
return data;
}
private:
node *next;
string data;
};
This is a much safer list node. All a user can interact with is the data. The rest is safely locked up and only exposed to list.
class list
{
public:
list()
{
head = NULL;
}
void insertAtEnd(string);
private:
node *head;
};
Unchanged, other than the stuff removed because it supported code not included in the question.
void list::insertAtEnd(string value)
{ //main func being used
node **cur = &head; // double pointer abstracts away need to test for head.
// Now all nodes are equal and we're always pointed at a next.
while (*cur != NULL && (*cur)->getData() != value) // note && not ||
//we loop until out of nodes unless we find a match
{
cur = &(*cur)->next; // get pointer to next next
}
if (*cur != NULL) // pointing at a node. Must have exited because of match
{
// did stuff I ommtted because no MCVE
}
else // not pointing at node. Need a new node.
{
*cur = new node(value);
}
}
Bloodbath. Rather than drop a big ball of explanation here, I commented inline what I was doing and why.