Why does my Template Linked List not work? - c++

Question

I can't specify what the problem is nor do I get any errors. This is my code:
Node.h:
#ifndef NODE_H
#define NODE_H
#include <iostream>
using namespace std;
template <typename T>
class LinkedList;
template <typename T>
class Node {
public:
Node(T data) : data(data),previousNode(nullptr),nextNode(nullptr) {}
Node<T>* GetNextNode() const {
return nextNode;
}
void SetNextNode(Node<T>* nextNode) {
this->nextNode = nextNode;
}
Node<T>* GetPreviousNode() const {
return previousNode;
}
void SetPreviousNode(Node<T>* previousNode) {
this->previousNode = previousNode;
}
T GetData() const {
return data;
}
void SetData(T data) {
this->data = data;
}
private:
T data;
Node<T>* previousNode;
Node<T>* nextNode;
};
#endif /* NODE_H */
linkedList.h:
#ifndef LINKEDLIST_H
#define LINKEDLIST_H
#include "node.h"
#include <stdexcept>
#include <iostream>
#include <booking.h>
using namespace std;
template<typename T>
class LinkedList {
public:
LinkedList() {
root = nullptr;
end = nullptr;
cursor = end;
}
void insertNode(T data) {
Node<T>* node = new Node<T>(data);
cerr << "entered insert node" << endl;
if (root == nullptr) {
root = node;
node->SetNextNode(end);
end->SetPreviousNode(node);
}else{
node->SetNextNode(cursor);
node->SetPreviousNode(cursor->GetPreviousNode());
if (cursor->GetPreviousNode())
cursor->GetPreviousNode()->SetNextNode(node);
cursor->SetPreviousNode(node);
}
cursor = node;
if (!cursor->GetPreviousNode())
root = cursor;
}
bool isAtEnd() {
return (cursor == end);
};
void step_back() {
if (cursor && cursor->GetPreviousNode()) {
cursor = cursor->GetPreviousNode();
}
}
void advance() {
if (cursor && cursor->GetNextNode()) {
cursor = cursor->GetNextNode(); }
};
T getNode() {
return cursor->GetData();
};
void reset() {
cursor = root;
};
void deleteNode() {
Node<T>* tmpPrevious;
Node<T>* tmpNext;
if (root == nullptr) {
throw underflow_error("empty list...");
} else {
if (cursor->GetPreviousNode() == nullptr) {
if (cursor->GetNextNode() == end) {
delete cursor;
root = nullptr;
end->SetPreviousNode(nullptr);
cursor = end;
} else {
cursor = cursor->GetNextNode();
delete (root);
cursor->SetPreviousNode(nullptr);
root = cursor;
}
} else {
if (cursor->GetNextNode() == end) {
tmpPrevious = cursor->GetPreviousNode();
delete cursor;
cursor = end;
end->SetPreviousNode(tmpPrevious);
tmpPrevious->SetNextNode(end);
} else {
tmpPrevious = cursor->GetPreviousNode();
tmpNext = cursor->GetNextNode();
delete cursor;
tmpPrevious->SetNextNode(tmpNext);
tmpNext->SetPreviousNode(tmpPrevious);
cursor = tmpNext;
}
}
}
return;
};
protected:
Node<T>* root;
Node<T>* cursor;
Node<T>* end;
};
#endif /* LINKEDLIST_H */
Booking.h
#ifndef BOOKING_H
#define BOOKING_H
class Booking{
private:
long bookingID;
public:
Booking(long bookingID);
long getBookingID();
};
#endif // BOOKING_H
Booking.ccp:
#include "booking.h"
Booking::Booking(long bookingID):bookingID(bookingID){}
long Booking::getBookingID(){
return bookingID;
}
main.cpp:
#include <QCoreApplication>
#include <cstdlib>
#include <linkedList.h>
#include <iostream>
#include <string>
#include <booking.h>
using namespace std;
int main(int argc, char *argv[]){
QCoreApplication a(argc, argv);
LinkedList<Booking*> allBookings;
Booking* booking1 = new Booking(12);
allBookings.insertNode(booking1);
long test = allBookings.getNode()->getBookingID();
cout << "test: " << test << endl; //doesn't print anything
return a.exec();
}
I didn't get any errors. cout << "test: " << test << endl; in the main.cpp doesn't execute, because I was expecting it to print something. What am I doing wrong here? I did some debugging and I think in my Node.h implementation the function SetPreviousNode doesn't execute when I'm trying to insert a node in the main.cpp.

Answer 1

This code in insertNode
if (root == nullptr) {
root = node;
node->SetNextNode(end);
end->SetPreviousNode(node);
}else{
end has a value of nullptr at when you reach end->SetPreviousNode(node); which is likely crashing your program. (You should be able to confirm that in your debugger).
I'd like to suggest a fix but it's not clear to me what you are trying to do. The code seems a little complex. Plus I don't like the design decision to include a cursor in the list. I would drop that if you are able to.