Creating objects with new in function and "this is nullptr" exception - c++

Question

I've been trying to make a template class (called List) which stores different type of objects. I created Base class to be like base in my program and Human class. Base can create new Human and to have access to them all, has a (private) pointer to List * first_h (in every List is stored Human* me, List * next and List * first_h (first_h in list)).
The problem is, when I add like more than 1 Human to my Base, I can't display them properly. I think it's because of creating new Human's in Base method (void Base::create_human(string name)) but everything I did don't work it out.
There are my classes:
class Human
{
private:
string name;
public:
Human(string name) { this->name = name; }
void display() { cout << "My name: " << name << endl; }
};
template <class T>
class List
{
private:
T* me;
List <T>* next;
List <T>* first;
public:
void set_me(T* me) { this->me = me; }
T* get_me() { return this->me; }
void set_next(List* next) { this->next = next; }
List <T>* get_next() { return this->next; }
void set_first(List* first) { this->first = first; }
List <T>* get_first() { return this->first; }
void add(T*& created);
void display();
};
class Base
{
private:
List <Human>* first_h;
public:
void set_first_h(List <Human>*& first) { this->first_h = first; }
List <Human>* get_first_h() { return this->first_h; }
void create_human(string name)
{
Human* created = new Human(name);
this->first_h->add(created);
}
};
and methods:
template <class T>
void List<T>::add(T*& created)
{
List <T>* temp = this->get_first();
List <T>* new_list;
if ((this->get_me()) == nullptr)
{
this->set_next(nullptr);
this->set_me(created);
this->set_first(this);
}
else
{
new_list = new List <T>;
temp = this->get_first();
while (temp != nullptr)
{
temp = temp->get_next();
}
new_list->set_next(nullptr);
new_list->set_first(this->get_first());
temp->set_next(new_list);
}
}
template <class T>
void List<T>::display()
{
List <T>* temp_list = this;
T* temp;
if (temp_list == nullptr)
{
std::cout << "There is nothing!" << endl;
}
while (temp_list != nullptr)
{
temp = temp_list->get_me();
temp->display();
temp_list = temp_list->get_next();
}
std::cout << "End!" << endl;
}
and my main function:
int main()
{
Base Main;
List <Human>* first_h = new List <Human>();
Main.set_first_h(first_h);
Main.create_human("Jane");
Main.create_human("John");
Main.create_human("Mary");
Main.get_first_h()->display();
system("pause");
return 0;
}
Sorry for my English and thank you in advance!
Edit:
I found out what was wrong:
in add function:
new_list->set_next(nullptr);
new_list->set_me(created);
new_list->set_first(this->get_first());
temp->set_next(new_list);
I forgot about:
new_list->set_me(created);
the mistake in add function as one of you wrote.

Answer 1

Your loop
while (temp != nullptr)
{
temp = temp->get_next();
}
runs till temp is nullptr and then you do
temp->set_next(new_list);
So, as you see, inside set_next() the this pointer is nullptr.
Please learn how to use a debugger and look at the call stack.