Clang error: pointer being freed was not allocated - c++

I wrote this implementation of Linked list:
template<typename T> // implementation: Linked_list
class Linked_list {
private:
Node<T>* head;
Node<T>* tail;
Node<T>* current;
int size;
void init()
{
head = tail = current = new Node<T>();
size = 0;
}
Node<T>* search_previous()
{
if (current == head) {
return nullptr;
}
Node<T>* previous_node = head;
while (previous_node->next != current) {
previous_node = previous_node->next;
}
return previous_node;
}
public:
Linked_list()
{
init();
}
void clear()
{
while (head != nullptr) {
current = head;
head = head->next;
delete current;
}
init();
}
~Linked_list()
{
clear();
delete head;
}
void append(T p_element)
{
tail->next = new Node<T>(p_element);
tail = tail->next;
++size;
}
void insert(T p_element)
{
current->next = new Node<T>(p_element, current->next);
if (current == tail) {
tail = tail->next;
}
++size;
}
T remove()
{
if (current->next == nullptr) {
throw std::runtime_error("No element to remove");
}
T removed_element = current->next->element;
Node<T>* temporary_pointer = current->next;
current->next = current->next->next;
if (temporary_pointer == tail) {
tail = current;
}
delete temporary_pointer;
--size;
return removed_element;
}
T get_element()
{
if (current->next == nullptr) {
throw std::runtime_error("No element to get");
}
return current->next->element;
}
void go_to_start()
{
current = head;
}
void go_to_end()
{
current = tail;
}
void go_to_pos(int p_pos)
{
if ((p_pos < 0) || (p_pos >= size)) {
throw std::runtime_error("Index out of bounds");
}
current = head;
for (int index = 0; index < p_pos; ++index) {
current = current->next;
}
}
void next()
{
if (current != tail) {
current = current->next;
}
else {
throw std::runtime_error("There's no next positition");
}
}
void previous()
{
if (current != head) {
current = search_previous();
}
else {
throw std::runtime_error("There's no previous positition");
}
}
int get_pos()
{
int pos = 0;
Node<T>* temporary_pointer = head;
while (temporary_pointer != current) {
temporary_pointer = temporary_pointer->next;
++pos;
}
return pos;
}
int get_size()
{
return size;
}
void concat(Linked_list<T> p_list)
{
for (p_list.go_to_start(); p_list.get_pos() < p_list.get_size(); p_list.next()) {
append(p_list.get_element());
}
}
};
And here's the node:
template<typename T>
class Node {
public:
T element;
Node<T>* next;
Node(T p_element, Node<T>* p_next = nullptr)
{
element = p_element;
next = p_next;
}
Node(Node<T>* p_next = nullptr)
{
next = p_next;
}
};
The problem that I have is that when I try to use the method concat I get this message from Clang:
proofs(13417,0x7fff7bb9f000) malloc: * error for object 0x7fe10b603170: pointer being freed was not allocated
* set a breakpoint in malloc_error_break to debug
Abort trap: 6
What can I do for fix it?

The obvious error is this:
void concat(Linked_list<T> p_list)
You are passing a Linked_list by value. That means that a temporary copy of the linked list is created and destroyed. Since the destructor deletes the memory, it is also deleting the memory of the linked list that you are making the copy of.
Since your Linked_list class does not have a user-defined assignment operator or copy constructor to handle the members that point to dynamically allocated memory, the class cannot be safely copied (if you debugged, you should have seen that a destructor was called that you didn't expect, and that is the temporary being destroyed, thus corrupting the original object).
To prevent this, either pass by reference (not value),
void concat(Linked_list<T>& p_list)
or provide appropriate copy constructor and assignment operator.
See What is the rule of Three

Related

C++ Queue Implementation using the Default Move Assignment Operator

My group and I attempted to implement a queue in C++ based on the following example for the code of a stack.
template<typename T>
class Stack {
private:
struct Node {
T data;
Node* next;
Node(T data, Node* next): data(data), next(next) {}
// No destructor here; it is a private inner class and would be slow
// to delete a chain of nodes this way!
};
private:
Node* head;
public:
Stack(): head(nullptr) {}
~Stack() {
while (head != nullptr) {
Node* old_head = head;
head = head->next; // update
delete old_head;
}
}
// Prohibit copy construction and copy assignment
Stack(Stack&) = delete;
Stack& operator=(Stack&) = delete;
// Wait wait I want to be able to move
Stack(Stack&&) = default;
Stack& operator=(Stack&&) = default;
public:
int getSize() {
int count = 0;
for (Node* n = head; n != nullptr; n = n->next) count++;
return count;
}
bool isEmpty() {
return head == nullptr;
}
void push(T x) {
head = new Node(x, head);
}
T pop() {
if (isEmpty()) {
throw underflow_error("Cannot pop from empty stack");
}
Node* nodeToDelete = head;
T poppedValue = head->data;
head = head->next;
delete nodeToDelete;
return poppedValue;
}
T peek() {
if (isEmpty()) {
throw underflow_error("Cannot peek into empty stack");
}
return head->data;
}
};
Just like the stack example, we attempted to implement move for the queue using the same ideas, including the default move assignment operator. Doing this, we came across problems such as invalid operands errors, collapsed stack frames and more when running our code.
template < typename T >
class Queue {
private:
struct Node {
T data;
Node * next;
Node(T data, Node * next): data(data), next(next) {}
};
private: Node * head;
private: Node * tail;
public:
Queue(): head(nullptr), tail(nullptr) {}~Queue() {
while (head != nullptr) {
Node * old = head;
head = head -> next;
delete old;
}
}
Queue(Queue & ) = delete;
Queue & operator = (Queue & ) = delete;
Queue(Queue && ) = default;
Queue & operator = (Queue && ) = default;
public:
int get_size() {
int count = 0;
for (Node * n = head; n != nullptr; n = n -> next)
count++;
return count;
}
bool isEmpty() {
return head == nullptr;
}
void enqueue(T x) {
Node * temp = new Node {x, nullptr};
if (head == nullptr) {
head = temp;
tail = temp;
} else {
tail -> next = temp;
tail = temp;
}
}
T dequeue() {
if (isEmpty()) {
throw underflow_error("Cannot dequeue from empty queue");
}
Node * nodeToDelete = head;
T poppedValue = head -> data;
head = head -> next;
delete nodeToDelete;
return poppedValue;
}
};
We ended up making our own move assignment operator which the queue worked as expected. The following code is what we ended up with.
Template <typename T>
class Queue {
private:
struct Node {
T data;
Node *next;
Node(T data, Node *next) : data(data), next(next) {}
};
private:
Node *head;
private:
Node *tail;
public:
Queue() : head(nullptr), tail(nullptr) {}
~Queue() {
while (head != nullptr) {
Node *old = head;
head = head->next;
delete old;
}
}
Queue(Queue &) = delete;
Queue &operator=(Queue &) = delete;
Queue(Queue &&) = default;
Queue &operator=(Queue &&other) {
if (&other == this) {
return *this;
}
delete head;
head = other.head;
tail = other.tail;
other.head = nullptr;
other.tail = nullptr;
return *this;
}
public:
int get_size() {
int count = 0;
for (Node *n = head; n != nullptr; n = n->next) {
count++;
}
return count;
}
bool is_empty() {
return head == nullptr;
}
void enqueue(T x) {
Node *temp = new Node{x, nullptr};
if (head == nullptr) {
head = temp;
tail = temp;
} else {
tail->next = temp;
tail = temp;
}
}
T dequeue() {
if (is_empty()) {
throw underflow_error("Cannot dequeue from empty queue");
}
Node *nodeToDelete = head;
T poppedValue = head->data;
head = head->next;
delete nodeToDelete;
return poppedValue;
}
Although we ultimately went with the latter implementation, we were really curious as to why the default move assignment operator worked for the stack and not the queue. We were wondering if it was because we created our own destructor for the class and disabled the copy operator, but we are unsure. Perhaps we were going about the implementation wrong? Any help/ feedback would be much appreciated!
Generally, you should always consider implement your own move assignment operator and move constructor when it comes to dynamic memory allocation.
Your stack one just appeared to work, but actually it is not correct.
Try to add these to your stack, and you will see the problem:
Stack <int> func() {
Stack <int> s;
s.push(3);
return s;
}
int main()
{
Stack <int> b;
b = func(); // assignment move
return 0;
}
func() is returning a Stack with non-null head member variable (this is critical)
When leaving func(), local variable s is destructed
When leaving main(), local variable b is destructed (problem here)
That's why this code causes a double-free problem in your Stack.
(BTW, your Queue assignment move operator may cause memory leak, since delete head; may not be what you want to do.)

Error with peek() function of a Stack class in c++

I am trying to implement the peek() function of a Stack class and have this issue where I cannot return the top object of the stack, but instead get an error. I have tried removing the & to the peek function and tried to set it to a const, but I still get errors. Would the issue be outside of this function? as I am not sure what else I can try to solve this problem.
Error:
LStack.h:55:28: error: cannot bind non-const lvalue reference of type ‘int&’
to
an rvalue of type ‘int’
return data.get_current();
LStack.h
#include "LinkedList.h"
#include <cstdlib>
#include <iostream>
template <typename T>
class LStack
{
public:
//mutator member functions
LStack(){}
~LStack(){}
void push(const T& obj) //insert obj at the top of the stack
{
data.add_to_head(obj);
numofstacks++;
}
T pop() //remove and return the top object from the stack, error if stack is empty
{
if (is_empty()){
std::cout << "Stack is empty";
}
else{
data.remove_from_head();
numofstacks--;
return data.get_current();
}
}
bool is_empty() const //return a boolean indicating whether the stack is empty
{
return (size() == 0);
}
//query member functions
int size() const //return the number of objects in the stack
{
return numofstacks;
}
//return a reference to the object at the top of the stack, NULL if the stack is empty, (also refered to as top())
T& peek()
{
if (is_empty()){
std::cout << "Stack is empty";
}
else{
//return top of the stack object
return data.get_current();
}
}
private:
LinkedList<T> data;
int used;
int numofstacks;
};
LinkedList.h
#include "Node.h"
#include <cstdlib>
#include <iostream>
template <typename T>
class LinkedList
{
public:
LinkedList() //constructor
{
head = NULL;
tail = NULL;
list_length=0;
}
~LinkedList()//destructor since we're creating the linked list on the heap
{
while (head != NULL)
{
remove_from_head();
}
tail = NULL;//not sure if in or out of while loop
}
LinkedList(T& item)
{
head = new Node<T>();
head->set_data(item);
tail = head;
list_length = 1;
}
void add_to_head(T item)
{
if (list_length == 0){ //if list is empty
head = new Node<T>();
head->set_data(item);
tail = head;
list_length = 1;
}
else //Else if list is not empty.. Insert node at the head
{
Node<T>* head_insert = new Node<T>();
head_insert->set_data(item);
head->set_prev(head_insert);
head_insert->set_next(head);
head = head_insert;
list_length++;
head_insert = NULL;
}
}
void add_to_tail(T item)
{
if (list_length == 0){
head = new Node<T>();
head->set_data(item);
tail = head;
list_length = 1;
}
else //insert node at tail
{
Node<T>* tail_insert = new Node<T>();
tail_insert->set_data(item);
tail->set_next(tail_insert);
tail_insert->set_prev(tail);
tail = tail_insert;
list_length++;
tail_insert = NULL;
}
}
void remove_from_head()
{
if (list_length == 0){
return;
}
else if (list_length == 1){
delete head;
head = NULL;
tail = NULL;
list_length--;
return;
}
else
{
Node<T>* temp_head = head;
head = temp_head->get_next();
delete temp_head;
list_length--;
temp_head = NULL;
}
}
void remove_from_tail()
{
if (list_length == 0){
return;
}
else if (list_length == 1)
{
delete head;
head = NULL;
tail = NULL;
list_length--;
return;
}
else
{
Node<T>* temp_tail = tail;
tail = temp_tail->get_prev();
delete temp_tail;
list_length--;
temp_tail = NULL;
}
}
std::size_t size()
{
return list_length;
}
T get_current() // RESULTS IN SEG ERROR
{
return current->get_data();
}
void forward()
{
current = current->get_next();
}
void back()
{
current = current->get_prev();
}
void move_to_head()
{
current = head;
}
void move_to_tail()
{
current = tail;
}
private: //private members
Node<T>* head; //point to start of list
Node<T>* tail; //point to end of list
Node<T>* current; //optional - used to refer to a node in our list
std::size_t list_length;
};
Would the issue be outside of this function? as I am not sure what else I can try to solve this problem.

Threads on xcode while compiling the c++ code

so I was trying to build this project on deque using the doubly linked list. but when I build it. it says build but gives threads and doesn't give the output as required.
I have re-implemented the major problem(copy constructor) and all the functions again and again but then it still gives me new threads every time.
this is the header file.
#pragma once
#include <stdexcept>
using namespace std;
class Node
{
public:
int data;
Node* next;
Node* previous;
Node();
Node(const int &x);
};
class Deque
{
public:
Deque();
Deque(const Deque &d);
Deque &operator= (const Deque &d);
~Deque();
void insertFront(const int &x);
void insertBack(const int &x);
int removeFront();
int removeBack();
int peekFront();
int peekBack();
bool empty() const;
int size()const;
friend ostream& operator << (ostream &out, const Deque &d);
private:
Node* front;
Node* rear;
};
this will be the .cpp (implementation file.)
//
// Deque_cmpt225.cpp
// Deque_cmpt225
//
// Created by Aryan Arora on 2017-10-09.
// Copyright © 2017 Aryan Arora. All rights reserved.
//
#include "Deque_cmpt225.h"
#include <iostream>
#include <stdexcept>
using namespace std;
Node:: Node()
{
previous = nullptr;
next = nullptr;
data = 0;
}
Node:: Node(const int &x)
{
Node();
data = x;
}
Deque:: Deque() //Empty Deque.
{
front = nullptr;
rear = nullptr;
}
Deque:: ~Deque()
{
if (this->empty())
return;
else{
Node* temp;
while (this->front->next != nullptr){
temp = this->front;
this->front = this->front->next;
delete temp;
}
temp = this->front;
this->front = nullptr;
this->rear = nullptr;
delete temp;
}
}
Deque:: Deque (const Deque &d) //Copy Constructor
{
if (d.empty()) //Deque is empty.
{
return;
}
Node* temp = d.front;
int x;
if (temp->next == nullptr) //Deque of just one node
{
x = temp->data;
Node *n1 = new Node (x);
n1->next = nullptr;
n1->previous = nullptr;
this->front = n1;
this->rear = n1;
}
else //Deque has more than one node
{
while (temp!= nullptr)
{
this->insertBack(temp->data);
temp = temp -> next;
}
}
}
Deque& Deque:: operator=(const Deque &d) //============================check again
{
if (this == &d)
return *this;
else
{
this->~Deque(); //DELETING THE DEQUE
Node* temp = d.front; //COPYING EACH NODE
while (temp != NULL)
{
this->insertBack(temp->data); //INSERTING AT THE BACK
temp = temp->next; //POINTING TEMP TO NEXT NODE
}
}
return *this;
}
void Deque:: insertFront(const int &x)
{
Node* temp = new Node(x);
temp->next = nullptr;
temp->previous = nullptr;
if (empty())
{
this->front = temp;
this->rear = temp;
}
else
{
temp->next = this->front;
temp->previous = nullptr;
this->front->previous = temp;
this->front = temp;
}
}
void Deque:: insertBack(const int &x)
{
Node* temp = new Node(x);
temp->next = nullptr;
temp->previous = nullptr;
if (empty())
{
this->front = temp;
this->rear = temp;
}
else
{
temp->next = nullptr;
temp->previous = this->rear;
this->rear->next = temp;
this->rear = temp;
}
}
int Deque:: removeFront()
{
if (empty()) //=================runtime error
{
throw std::runtime_error("The que is empty.");
}
else{
Node* temp;
temp = this->front;
int x = temp->data;
if ( this->front->next != nullptr )
{
this->front = this->front->next;
this->front->previous = nullptr;
}
else
{
this->front = nullptr;
this->rear = nullptr;
}
delete temp;
return x;
}
}
int Deque:: removeBack()
{
if (empty()) //=================runtime error
{
throw std::runtime_error("The que is empty.");
}
else{
Node* temp = this->rear;
int x = temp->data;
if ( this->rear->previous != nullptr )
{
this->rear = this->rear->previous;
this->rear->next = nullptr;
}
else
{
this->rear = nullptr;
this->front = nullptr;
}
delete temp;
return x;
}
}
int Deque:: peekFront()
{
if (empty()) //=================runtime error
{
throw std::runtime_error("The que is empty.");
}
else
{
return this->front->data;
}
}
int Deque:: peekBack()
{
if (empty()) //=================runtime error
{
throw std::runtime_error("The que is empty.");
}
else
{
return this->rear->data;
}
}
bool Deque:: empty() const
{
if (this->front == nullptr && this->rear == nullptr)
return true;
else
return false;
}
int Deque:: size() const
{
Node* temp = this->front;
int count = 0;
while (temp != nullptr)
{
count++;
temp = temp->next;
}
return count;
}
ostream& operator << (ostream &out, const Deque &d)
{
Node* temp = d.front;
out << "NULL -> ";
while (temp != nullptr)
{
out << temp->data << " <-> ";
temp= temp->next;
}
out << "<- NULL" << endl;
return out;
}
thanks in advance.
Your code has many problems..
Your Node constructor doesn't delegate properly..
Node::Node()
{
previous = nullptr;
next = nullptr;
data = 0;
}
Node::Node(const int &x)
{
Node(); //Creates a temporary node that gets destroyed immediately..
data = x;
}
It's much simpler if you change it to:
Node::Node() : Node(0) //Delegating constructor.
{
}
Node::Node(const int &x) : previous(nullptr), next(nullptr), data(x)
{
}
This point isn't really a problem, but worth mentioning.. You keep setting the Node pointers to nullptr right after construction. This is not necessary because your constructor already does that..
Node* temp = new Node(x);
temp->next = nullptr; //Not needed anymore with the above fixes.
temp->previous = nullptr; //Not needed anymore with the above fixes.
You never initialize your variables in the copy constructor..
In your constructor, you have (I changed it, but it has the same meaning):
Deque::Deque() : front(nullptr), rear(nullptr)
{
}
But in your copy constructor, you have:
Deque::Deque(const Deque &d)
{
//Other code here.. You never initialized front and rear to nullptr..
}
You never set front and rear to nullptr so empty() returns false since they are a "random" uninitialized value.. Then in insertBack you go on to access this and boom.. Access Violation.
To fix it, you do:
Deque::Deque(const Deque &d) : front(nullptr), rear(nullptr)
{
//Other code here..
}
Next issue is that your copy assignment operator is calling the destructor!
Deque& Deque::operator=(const Deque &d)
{
if (this == &d)
return *this;
else
{
this->~Deque() //YOU CANNOT DO THIS.. Create a private member function for cleaning up.. Then call that function in your destructor and call that function here.. You cannot invoke the destructor like this.
}
//....
}

Linked List Copy Constructor | Undefined Behavior

I've been building on a template Linked List and recently implemented a user-defined copy constructor to handle deep copies of my Linked List. My current solution compiles just fine but when I execute, nothing is displayed.
#include <iostream>
template<typename T>
class LinkedList
{
private:
struct Node
{
T data;
Node* next;
};
Node* head;
Node* tail;
int size;
public:
LinkedList();
LinkedList(const LinkedList<T> &list);
~LinkedList();
LinkedList<T>& operator=(const LinkedList<T> list);
int getSize() const;
void display() const;
void push(const T &data);
void insert(const int pos, const T &data);
void remove(const int pos);
};
template<typename T>
LinkedList<T>::LinkedList() : head{ nullptr }, tail{ nullptr }, size{ 0 }
{
}
// TODO: User-defined copy constructor
template<typename T>
LinkedList<T>::LinkedList(const LinkedList<T> &list)
: head{ nullptr }, tail{ nullptr }, size{list.size}
{
std::cout << "In the copy constructor\n";
if (list.head == nullptr)
{
return;
}
else
{
Node* curNode = new Node{list.head->data, nullptr};
head = curNode; // sets the head member variable to first node in Linked List
Node* curListNode = list.head;
while (curListNode->next != nullptr)
{
curNode->next = new Node{curListNode->next->data, nullptr};
curListNode = curListNode->next;
curNode = curNode->next;
}
curNode->next = new Node{curListNode->next->data, nullptr};
tail = curNode->next;
}
}
template<typename T>
LinkedList<T>::~LinkedList()
{
Node* prevNode = head;
Node* curNode = head;
while(curNode != nullptr)
{
prevNode = curNode;
curNode = curNode->next;
delete prevNode;
}
head = nullptr;
tail = nullptr;
}
template<typename T>
LinkedList<T>& LinkedList<T>::operator=(const LinkedList<T> list)
{
// make a copy of each node - much like the copy constructor
std::cout << "In the overloaded assignment\n";
}
template<typename T>
int LinkedList<T>::getSize() const
{
return size;
}
template<typename T>
void LinkedList<T>::display() const
{
Node* curNode = head;
while (curNode != nullptr)
{
std::cout << curNode->data << '\n';
curNode = curNode->next;
}
std::cout << '\n';
}
template<typename T>
void LinkedList<T>::push(const T &data)
{
Node* newNode = new Node{data, nullptr};
if (size == 0)
{
head = newNode;
tail = newNode;
}
else
{
tail->next = newNode;
tail = newNode;
}
++size;
}
template<typename T>
void LinkedList<T>::insert(const int pos, const T &data)
{
if (pos < 0 || pos > size)
{
throw "Index is out of range!";
}
else if (pos == size)
{
push(data);
}
else
{
Node* newNode = new Node{data, nullptr};
Node* prevNode = head;
Node* curNode = head;
int i = 0;
while (i != pos)
{
prevNode = curNode;
curNode = curNode->next;
++i;
}
prevNode->next = newNode;
newNode->next = curNode;
++size;
}
}
template<typename T>
void LinkedList<T>::remove(const int pos)
{
if (pos < 0 || pos > size)
{
throw "Index is out of range!";
}
else if (size == 0)
{
throw "List is empty!";
}
else
{
Node* prevNode = head;
Node* curNode = head;
int i = 1;
while (i != pos)
{
prevNode = curNode;
curNode = curNode->next;
++i;
}
prevNode->next = curNode->next;
delete curNode;
if (pos == size)
{
tail = prevNode;
}
--size;
}
}
int main()
{
LinkedList<int> list;
list.push(1);
list.push(3);
list.push(6);
list.display();
LinkedList<int> copyList{list};
copyList.display();
return 0;
}
The first LinkedList<int> list doesn't even display when I add the the copyList statement to main(). However, when I comment out the two copyList statements, list displays as normal.
I added print statements to see if either the copy constructor or the operator= functions were being called and neither of those are printed to the console when the copyList statements are added to my program (the code compiles just fine).
I could use any help to help diagnose what's causing this behavior.
A simple copy constructor like this one should suffice:
template<typename T>
LinkedList<T>::LinkedList(const LinkedList<T> &list)
: head{ nullptr }, tail{ nullptr }, size{0}
{
std::cout << "In the copy constructor\n";
Node* curNode = list.head;
while (curNode != nullptr)
{
this->push(curNode->data);
curNode = curNode->next;
}
}
Note that this is just your display method rewritten to insert elements in the current list.

Linked list outputting different values to cout

I'm writing a linked list container for my homework. Using Qt 4.7 and gcc 4.4, I've found some problems in the code that I guess they are related to memory management or garbage collection.
After using the << operator to display the list, all data of list is changed. for example, after construction and setting a list like l,
std::cout<<l<<std::endl;
std::cout<<l<<std::endl;
prints:
Data = [-10, 3, 2, 8, 1, -1, -2, ] // this is correct
Data = [0, 149560240, 149560192, 149558336, 149560256, 149558320, 149560208, ]
My linked list is:
#ifndef LINKEDLIST1_H_
#define LINKEDLIST1_H_
#include <iostream>
template<class T> class LinkedList1;
template<class T> class Node;
template<class T>
class Node
{
friend class LinkedList1<T> ;
public:
Node(const T& value) :
Data(value), Next(NULL)
{
}
Node() :
Next(NULL)
{
}
T Data;
Node* Next;
};
template<class T>
class LinkedList1
{
public:
LinkedList1() :
size(-1), first(NULL)
{
}
~LinkedList1()
{
Node<T>* i = this->first;
Node<T>* j = this->first;
while(j!=NULL)
{
j=i->Next;
delete i;
i=j;
}
}
// Operations on LinkedList
Node<T>* First()
{
return first;
}
int Size()
{
return size + 1;
}
int Count()
{
int size = 0;
Node<T>* current = this->firstFirst();
while(current != NULL)
{
size++;
current = current->Next;
}
this->size = size;
return this->Size();
}
bool IsEmpty()
{
return this->Size() == 0;
}
void Prepend(Node<T>* value) //O(1)
{
value->Next = this->first;
this->first = value;
this->size++;
}
void Prepend(const T& value) //O(1)
{
Node<T>* item = new Node<T>(value);
item->Next = this->first;
this->first = item;
this->size++;
}
void Append(Node<T>* value)
{
if(this->IsEmpty())
{
this->first = value;
this->size++;
}
else
{
Node<T>* current = this->First();
while(current->Next != NULL)
current = current->Next;
current->Next = value;
value->Next = NULL;
this->size++;
}
}
void Append(const T& value)
{
Node<T>* temp= new Node<T>(value);
this->Append(temp);
}
void Insert(Node<T>* location, Node<T>* value) //O(n)
{
Node<T>* current = this->first;
Node<T>* before = current;
while(current != NULL)
{
before = current;
current = current->Next;
if(current == location)
{
before->Next = value;
value->Next = current;
this->size++;
break;
}
}
}
void Insert(Node<T>* location, const T& value)
{
Node<T>* temp = new Node<T>(value);
this->Insert(location,temp);
}
Node<T>* Pop()
{
if(this->IsEmpty())
return NULL;
else
{
Node<T>* current = this->first;
Node<T>* before = current;
while(current->Next != NULL)
{
before = current;
current = current->Next;
before->Next = current;
}
before->Next = NULL;
this->size--;
return current;
}
}
Node<T>* PopF()
{
if(!this->IsEmpty())
{
Node<T>* head = this->first;
this->first = this->first->Next;
this->size--;
return head;
}
else
return NULL;
}
Node<T>* Remove(Node<T>* location)
{
// validating by IsEmpty is not necessary for this operation,
// while statement's condition guarantees validation
Node<T>* current = this->first;
Node<T>* before = current;
while(current != NULL)
{
before = current;
current = current->Next;
before->Next = current;
if(current == location)
{
before->Next = current->Next;
current->Next=NULL;
return current;
}
}
return NULL; // Not found...
}
void Inverse()
{
if(this->IsEmpty())
return;
else
{
Node<T>* r = NULL;
Node<T>* q = this->first;
Node<T>* p = this->first;
while(q != NULL)
{
p = p->Next;
q->Next = r;
r = q;
q = p;
}
this->first = r;
}
}
// Ordered insertion. implement this: foreach i,j in this; if i=vale: i+=vale, break; else if i<=value<=j: this.insert(j,value),break
friend std::ostream& operator<<(std::ostream& out, const LinkedList1 item)
{
out<<"Data = [";
Node<T>* current = item.first;
while(current != NULL)
{
out << current->Data << ", ";
current = current->Next;
}
out<<"]";
return out;
}
void HelperOutput(std::ostream& out, const LinkedList1 item) const
{
out<<item;
}
Node<T>* operator[](const int& index)
{
int i=0;
Node<T>* current = this->first;
while(i<=index && current!=NULL)
{
if(i=index)
return current;
else
{
i++;
current=current->Next;
}
}
}
public:
int size;
Node<T>* first;
};
#endif /* LINKEDLIST1_H_ */
friend std::ostream& operator<<(std::ostream& out, const LinkedList1 item)
{
out<<"Data = [";
Node<T>* current = item.first;
while(current != NULL)
{
out << current->Data << ", ";
current = current->Next;
}
out<<"]";
return out;
}
first item in output of second call is always 0. So I Thinked I've set first to NULL in somewhere in code; but I checked out all of methods and there was nothing like that. In addition, printed value is not the pointer itself; it's pointer's Data. Somewhere somebody changes Datas of all Node<T>*s in my list.
Is this a memory management or garbage collection issue? if not, what I'm doing wrong?
One thing that stands out here is that your signature is:
std::ostream& operator<<(std::ostream& out, const LinkedList1 item)
Instead of:
std::ostream& operator<<(std::ostream& out, const LinkedList1& item)
So, you are invoking a copy of your LinkedList. I suspect the issue here is that you have not correctly implemented your copy and assignment operators for LinkedList1, such that the the copy references the original content, and the destructor is making the original object into garbage.
I would recommend adding the following to your definition of LinkedList1:
private:
// The following declarations disallow copy and assignment. Do not implement.
LinkedList1(const LinkedList1&);
LinkedList1& operator=(const LinkedList1&);
Adding the above will lead to linker errors for the original signature that you had. I would then recommend passing the linked list by const reference, and your problem should disappear.
As an aside, I notice that many of your functions can be made const but aren't. For example, you have int Size() instead of int Size()const. One should generally mark as const anything that can be so-marked. This is known as "const-correctness" and can avoid a large number of issues.
Also, minor style nitpick: you have if...else statements where one has braces and the other doesn't. I would strongly recommend that you use braces in all cases as this leads to more readable code.