_CtrlsValidHeapPointer(Block) - c++

Question

I'm new to c++ and I use c++ to learn data structure recently. I stuck when the error occurs, I've tried to debug but It's still confused me. So, this error is I try to implement two operations concatenate and merge, my terminal shows the result that seems to successful on logical. However, the error is coming in the next second.
Just like img:enter image description here call stack
Here is my code. Hopefully, someone can help me solve this issue, thanks!
#pragma once
#include <iostream>
using namespace std;
class LinkedList;
class Node
{
private:
int data;
Node* next;
public:
friend class LinkedList;
};
class LinkedList
{
private:
Node* first;
Node* last;
Node* third;
public:
LinkedList()
{
first = nullptr;
last = nullptr;
third = nullptr;
}
LinkedList(int A[], int n);
~LinkedList();
void Display();
void RDisplay();//Recursive
void RDisplay(Node* p);
Node* getFirstNode();
int Count();
int RCount(Node* p);//Recursive
int Sum();
int RSum(Node* p);//Recursive
int Max();
int RMax(Node* p);//Recursive
int LSearch(int key); //linear search
int RSearch(int key);
int RSearch(Node* p, int key);
void Insert(int position, int x);
void InsertLast(int x);
void SortedInsert(int x);
int Delete(int position);
int isSorted();
void RemoveDuplicate();
void ReverseE();//Elements
void ReverseL();//Links
void RReverse();//Recursive
void RReverse(Node* q,Node *p);
void Concatenate(Node* second);
void Merge(Node *second);
int Mid();
int isLoop();
};
//cpp file
#include "Linkedlist.h"
#include <iostream>
using namespace std;
LinkedList::LinkedList(int A[], int n)
{
Node* t ;
first = new Node;
first->data = A[0];
first -> next = nullptr;
last = first;
for (int i = 1; i < n; i++)
{
t = new Node;
t->data = A[i];
t->next = nullptr;
last->next = t;
last = t;
}
}
LinkedList ::~LinkedList()
{
Node* p = first;
while (first)
{
first = first->next;
delete p;
p = first;
}
}
void LinkedList::Merge(Node* second)
{
Node* last;
if (first->data < second->data)
{
third = first;
last = first;
first = first->next;
last->next = nullptr;
}
else
{
third = last = second;
second = second->next;
last->next = NULL;
}
while (first != NULL && second != NULL)
{
if (first->data < second->data)
{
last->next = first;
last = first;
first = first->next;
last->next = NULL;
}
else
{
last->next = second;
last = second;
second = second->next;
last->next = NULL;
}
}
if (first != NULL)
{
last->next = first;
first = third;
}
else
{
last->next = second;
first = third;
}
}
//concatenate
void LinkedList::Concatenate(Node* second)
{
Node* p = first;
while (p->next != NULL)
{
p = p->next;
}
p->next = second;
}
void LinkedList::Display()
{
Node* p = first;
while (p != nullptr)
{
cout << p->data << " -> ";
p = p->next;
}
}
Node* LinkedList::getFirstNode()
{
return first;
}
#include <iostream>
#include "Linkedlist.h"
#include "Circular.h"
#include "Doubly.h"
#include "CircularDoubly.h"
int main()
{
int A[] = { 1,2,3,4,6,7 };
int B[] = { 5,6,7,8 };
LinkedList c1(A,6);
LinkedList c2(B, 4);
c1.Concatenate(c2.getFirstNode());
c1.Display();
}
Should I offer more detail?
stack call
stack call2

Answer 1

Yes it's the problem in destructor, after Concatenate, the c2 list has been appended to c1 list, the elements are destroyed twice, once in c1's destructor, the second time in c2's destructor. This is a memory issue that may lead to a crash.
I suggest fix it like this:
Transfer the ownership to c1, then we avoid destroy twice
Node* LinkedList::ReleaseFirst() {
Node* tmp = first;
first = nullptr;
return tmp;
}
c1.Concatenate(c2.ReleaseFirst());
Online demo