Adding new Node to a linked list with two classes - c++

Question

When trying to add a new Node to the liked list it gives me a Segmentation fault. Can someone tell me what is wrong in the implementation of the addBook() function. I am not sure if it's the implementation of the function that is wrong, or the way that I've declared the classes.
class Reservation {
public:
int getID();
string getResevNum();
void setId(int x);
void setReseNum(string y);
private:
int ID;
string reservedNumber;
};
class ReservationCollection {
public:
ReservationCollection();
~ReservationCollection();
int getUserId(int &id);
string getUserBook(string &bookCall);
void findReservation();
void display();
void addBook(int id, string book);
void RemoveBook();
void ShutDown();
private:
struct Node {
Reservation *data;
Node *next;
};
Node *head;
};
ReservationCollection::ReservationCollection() {
Node *head = new Node;
head->next = NULL;
}
ReservationCollection::~ReservationCollection() {
}
void ReservationCollection::addBook(int id, string book){
Node *tmp = new Node;
tmp->data->setId(id);
tmp->data->setReseNum(book);
tmp->next = head->next;
head->next = tmp;
cout <<"Good\n";
}
int Reservation::getID(){
return ID;
}
string Reservation::getResevNum(){
return reservedNumber;
}
void Reservation::setId(int x){
ID = x;
}
void Reservation::setReseNum(string y){
reservedNumber = y;
}
int ReservationCollection::getUserId(int &id){
cout << "Enter Id number " << endl;
cin >> id;
return id;
}
string ReservationCollection::getUserBook(string &bookCall){
cout << "Enter book reservatin " << endl;
cin >> bookCall;
return bookCall;
}
int main()
{
int ID;
string BookNum;
char cmd;
do {
cout << "Enter command: ";
cin >> cmd;
ReservationCollection list;
if (cmd == 'A' || cmd == 'a'){
list.getUserId(ID);
list.getUserBook(BookNum);
list.addBook(ID, BookNum);
}
else if (cmd == 'S' || cmd == 's'){
cout << " list";
}
} while (cmd != 'Q' || cmd == 'q');
}

Answer 1

Wish I could just comment this:
All instances of the line Node *tmp = new Node; should read Node *tmp = new Node();

Answer 2

Don't use pointers if you don't have to. In this example Node has to be a pointer, because the list may have zero nodes, or 1000 nodes, so we need pointers to dynamically allocate memory on demand.
But (Reservation)data does not have to be a pointer. Each node always has one Reservation member.
If you do declare it as pointer then you must allocate it, and free it when it is no longer needed.
head should be initialized to NULL, because the single linked-list has no nodes when it is initialized. The first node inserted becomes the head.
#include <iostream>
#include <string>
using namespace std;
class Reservation
{
private:
int ID;
string reservedNumber;
public:
int getID() { return ID; }
string getResevNum() { return reservedNumber; }
void setId(int x) { ID = x; }
void setReseNum(string y) { reservedNumber = y; }
};
class ReservationCollection
{
public:
struct Node
{
Reservation data;
Node *next;
};
ReservationCollection();
~ReservationCollection();
void addBook(int id, string book);
Node* getHead() { return head; }
private:
Node *head;
};
ReservationCollection::ReservationCollection()
{
head = NULL;
}
ReservationCollection::~ReservationCollection()
{
Node *p = head;
while (p)
{
Node *next = p->next;
cout << "delete: " << p->data.getID() << ", " << p->data.getResevNum() << endl;
delete p;
p = next;
}
}
void ReservationCollection::addBook(int id, string book)
{
Node *node = new Node;
node->data.setId(id);
node->data.setReseNum(book);
//this element is the last element
node->next = NULL;
if (!head)
{
//first element inserted
head = node;
head->next = NULL;
}
else
{
//find the previous node in the list
Node *prev = head;
while (prev->next)
prev = prev->next;
//this node is after previous node
prev->next = node;
}
cout << "Good\n";
}
int main()
{
ReservationCollection list;
list.addBook(0, "Book0");
list.addBook(1, "Book1");
list.addBook(2, "Book2");
list.addBook(3, "Book3");
ReservationCollection::Node *p = list.getHead();
while (p)
{
ReservationCollection::Node *next = p->next;
cout << p->data.getID() << ", " << p->data.getResevNum() << endl;
p = next;
}
}

Answer 3

Creating a Node wont create the structure that Reservation *data; tries to point to, and so you try to access non initialized memory.
You need to initialize data:
tmp->data = new Reservation();