Reputation: 831
I'm writing my own linked list class (for educational purposes) and here it is:
My code
#include <iostream>
using namespace std;
#define PRINT(x) #x << " = " << x << " "
struct ListNode {
int val;
ListNode* next = nullptr;
ListNode(int x) : val(x), next(nullptr) {}
};
class LinkedList {
private:
ListNode* _head;
unsigned long long int _size;
public:
LinkedList() :_head(nullptr), _size(0) {}
LinkedList(ListNode* _h) :_head(_h), _size(0) {
ListNode* node = _head;
while (node != nullptr) {
_size++;
node = node->next;
}
}
// Copy constructor
LinkedList(const LinkedList& obj) {
ListNode* node = obj._head;
while (node != nullptr) {
this->add(node->val);
node = node->next;
}
}
~LinkedList() {
while (_head != nullptr) {
remove();
}
}
void add(const int& value) {
ListNode* node = new ListNode(value);
node->next = _head;
_head = node;
_size++;
}
int remove() {
int v = _head->val;
ListNode* node = _head;
_head = _head->next;
delete node;
_size--;
return v;
}
void print() {
if (size() == 0) {
cout << "List is empty" << endl;
return;
}
ListNode* node = _head;
while (node->next != nullptr) {
cout << node->val << " -> ";
node = node->next;
}
cout << node->val << endl;
}
unsigned long long int size() { return _size; }
ListNode* head() { return _head; }
};
int main() {
LinkedList L;
L.add(4);
L.add(3);
L.add(2);
L.add(1);
L.print();
LinkedList L2(L);
return 0;
}
The problem is that when I run this code, I get this error: error for object 0x7fff5b8beb80: pointer being freed was not allocated
I don't understand why. My logic beyond the copy constructor is simple: I iterate over the list I'm copying, which is obj
, and I add a new element to this
list, which is the list I'm copying to. Since my add()
function creates a new element with, well, new
, I can't see where my two lists share an element which I'm trying to delete twice in the destructor. What am I doing wrong?
Upvotes: 2
Views: 167
Reputation: 1368
You forgot to initialize your _head
in copy constructor:
// Copy constructor
LinkedList(const LinkedList &obj) {
_head = NULL; // <- Add This
ListNode *node = obj._head;
while (node != nullptr) {
this -> add(node -> val);
node = node -> next;
}
}
Upvotes: 6