C++ XOR linked list, deleting data - c++

Question

I have to do XOR linked list. Now im at point that i want to proper way clear memory. I did something like this but it seems doesnt work.
Minimal code i could add to work
void deleteAll(Data* head)
{
if (head == NULL)
cout << "Empty list." << endl;
else
{
if (XOR(head, NULL) == NULL)
{
Data* tmp = NULL;
Data* next;
while (head)
{
next = XOR(head->npx, tmp);
tmp = head;
delete head;
//cout << head->liczba << endl; EDIT <<< this line is not problem
head = next;
}
}
}
}
This is the moment when i alocate data
Data* tmp = new Data;
tmp->liczba = num;
tmp->npx = XOR(*head, NULL);
if (*head != NULL)
{
(*head)->npx = XOR(XOR((*head)->npx,NULL),tmp);
}
*head = tmp;
tmp = NULL;
delete tmp;
In main function after deleting function i run printAll function, then i can see that data has not been cleared.
Edit:
#include <iostream>
using namespace std;
struct Data {
int liczba;
Data* npx;
};
struct Data* XOR(struct Data* prev, struct Data* next)
{
return (Data*)((uintptr_t)(prev) ^ (uintptr_t)(next));
}
void pushEnd(Data** head, int num)
{
Data* tmp = new Data;
tmp->liczba = num;
tmp->npx = XOR(*head, NULL);
if (*head != NULL)
{
(*head)->npx = XOR(XOR((*head)->npx,NULL),tmp);
}
*head = tmp;
tmp = NULL;
delete tmp;
}
void printBackward(Data* head)
{
if (head == NULL)
cout << "Pusta lista." << endl;
else
{
Data* next;
Data* prev = NULL;
while (head)
{
cout << head->liczba << endl;
next = XOR(head->npx, prev);
prev = head;
head = next;
}
}
}
void deleteAll(Data* head)
{
if (head == NULL)
cout << "Empty list." << endl;
else
{
if (XOR(head, NULL) == NULL)
{
Data* tmp = NULL;
Data* next;
while (head)
{
next = XOR(head->npx, tmp);
tmp = head;
delete head;
head = next;
}
}
}
}
int main()
{
Data* head = NULL;
pushEnd(&head, 5);
pushEnd(&head, 10);
pushEnd(&head, 7);
pushEnd(&head, 3);
printBackward(head);
cout << head->liczba;
cout <<endl<< "DEL" << endl;
deleteAll(head);
printBackward(head);
}

Answer 1

In deleteAll you have a line preventing all deletions:
if(XOR(head, NULL) == NULL) { // remove this line
Your deleteAll functions also takes a Data* and all changes you make to head will be local to the function only. A minimal change needed that should make it work is to take head as a Data*& - that is, a reference to a pointer, so that all changes to do to head in your function are actually made to the head you defined in main.
Example:
void deleteAll(Data*& head) {
if(head == nullptr)
cout << "Empty list." << endl;
else {
Data* tmp = nullptr;
Data* next;
while(head) {
next = XOR(head->npx, tmp);
tmp = head;
delete head;
head = next;
}
}
}
You still call it the same way: deleteAll(head);.
If you prefer calling it with deleteAll(&head); you could define the function like this:
void deleteAll(Data** head) {
if(*head == nullptr)
cout << "Empty list." << endl;
else {
Data* tmp = nullptr;
Data* next;
while(*head) {
next = XOR((*head)->npx, tmp);
tmp = *head;
delete *head;
*head = next;
}
}
}