Linked List Copy/Move semantic C++ - c++

Question

so I have this code for linked list below. I need to create copy/move constructors and operators.
I am having troubles how to make it the right way.
I know the code isn't perfect, I will appreciate all tips, but I want to focus mainly on copy/move semantic.
#include <iostream>
#include <string>
#include <stdexcept>
using namespace std;
class List {
class Node {
Node* next;
string text;
int index;
friend class List;
public:
Node(const string& value, int i) : next(nullptr), index(i), text(value) {}
friend ostream& operator<< (ostream& wy, const Node& wzl) {
if (wzl.next) return wy << wzl.text << ", " << *wzl.next;
else return wy << wzl.text;
}
};
Node* head;
int _size(Node* node, int size = 0) {
if (node == NULL) {
return size;
} else {
_size(node->next, size+1);
}
}
void _insert(Node* node, const string& value, int index) {
if (node->next == NULL || node->next->index > index) {
if (node->index == index) {
node->text = value;
} else {
Node* element = new Node(value, index);
element->next = node->next;
node->next = element;
}
} else {
_insert(node->next, value, index);
}
}
string _read(Node* node, int index) {
if (node->next != NULL && node->next->index <= index) {
return _read(node->next, index);
} else if (node->index == index) {
return node->text;
} else {
throw invalid_argument("No such index");
}
}
void _remove(Node* node, int index) {
if (node->next != NULL && node->next->index < index) {
_remove(node->next, index);
} else if (node->next->index == index) {
Node* temp;
if (node->next->next != NULL) {
int temp_index = node->next->next->index;
temp = new Node(node->next->next->text, temp_index);
if (node->next->next->next != NULL) {
temp->next = node->next->next->next;
} else {
temp->next = NULL;
}
temp->index = node->next->next->index;
} else {
temp = nullptr;
}
delete node->next;
node->next = temp;
} else {
throw invalid_argument("No such index");
}
}
public:
List() : head(nullptr){};
List(const List &lst) : head(nullptr) {
Node* tmp_lst = lst.head;
Node* tmp_this = this->head;
while (tmp_lst != NULL) {
// cerr << this->head->text;
tmp_this = new Node(tmp_lst->text, tmp_lst->index);
tmp_this = tmp_this->next;
tmp_lst = tmp_lst->next;
}
}
List(List&& lst);
List(initializer_list<string> lst) : List() {
Node* tmp;
int pos = 0;
for (auto element : lst) {
if (this->head != NULL){
tmp->next = new Node(element, pos);
tmp = tmp->next;
pos++;
} else {
this->head = new Node(element, pos);
tmp = this->head;
pos++;
}
}
};
List& operator= (const List& lst) {
if (this != &lst) {
delete this->head;
this->head = nullptr;
Node* tmp_lst = lst.head;
Node* tmp_this = this->head;
while (tmp_lst != NULL) {
tmp_this = new Node(tmp_lst->text, tmp_lst->index);
tmp_this = tmp_this->next;
tmp_lst = tmp_lst->next;
}
}
return *this;
}
List& operator= (List&& lst);
~List(){
delete head;
};
void insert(const string& value, int pos) {
if (pos < 0) {
throw invalid_argument("Position cant be negative");
}
if (this->head == NULL) {
Node* new_head = new Node(value, pos);
this->head = new_head;
} else if (this->head->index > pos) {
Node* new_head = new Node(value, pos);
new_head->next = this->head;
this->head = new_head;
} else {
_insert(this->head, value, pos);
}
}
string read(int pos) {
return _read(this->head, pos);
}
int size() {
return _size(this->head);
}
void remove(int pos) {
return _remove(this->head, pos);
}
public:
friend ostream& operator<< (ostream& wy, const List& lst) {
if (lst.head) return wy << "(" << *lst.head << ")";
else return wy << "()";
}
};
int main() {
return 0;
}

Answer 1

You List copy-constructor is severely flawed:
You initialize tmp_this to the value of this->head which is a null pointer
The above doesn't matter because the first thing you do in the loop is reassign tmp_this to point to a new Node object.
Then you immediately discard that pointer, by reassigning tmp_this to point to tmp_this->next which is a null pointer.
And you don't link anything into the list.
A working function could look something like
List(const List &lst) : head(nullptr) {
Node* tmp_lst = lst.head;
Node** tmp_current = &head;
while (tmp_lst != NULL) {
Node* tmp_this = new Node(tmp_lst->text, tmp_lst->index);
// Would prefer to use the copy-constructor here too, instead of the above
// Node* tmp_this = new Node(tmp_lst);
// This links the new node into the end of the list
*tmp_current = tmp_this
tmp_current = &tmp_this->next;
tmp_lst = tmp_lst->next;
}
}