Segmentation fault (C++ pointers) - c++

Question

I'm trying to implement a linked list class in C++ using a node class and a pointer to the next node.
template<class T>
class Node {
public: T val;
public: Node* next;
public: Node() { }
public: Node(T val) { this.val = val; }
};
I created a linked list class with a pointer to the head and a function append to add nodes to the list:
template<class T>
class LinkedList {
private: Node<T>* head;
public: LinkedList() { }
public: LinkedList(T val) { head -> val = val; }
public: void append(T val) {
Node<T>* temp = head;
while(temp -> val != NULL) {
temp = temp -> next;
}
temp -> val = val;
}
};
but after compilation and running, it throws this error "Segmentation fault (core dumped)"
I know a little about segmentation fault like trying to access a memory location that is no longer existed but I don't get it in this example, any help??

Answer 1

The main problem is that you don't initialize the next pointer with null pointer, but you assume it is null pointer by default. Here's how you fix it:
template <class T>
class Node {
public:
T val;
Node* next;
Node( T val_ = {} )
: val{ val_ }
, next{ nullptr }
{ }
};
Besides that, in the append there are problems. Here's how the code should have looked like completely:
template <class T>
class Node {
public:
T val;
Node* next;
Node(T val_ = {}) : val{ val_ }, next{ nullptr } {}
};
template <class T>
class LinkedList {
private:
Node<T>* head;
public:
LinkedList(T val_ = {}) : head{ new Node{val_} } {}
void append(T val) {
Node<T>* temp = head;
while (temp->next != nullptr) {
temp = temp->next;
}
temp->next = new Node<T>{ val };
}
};
int main() {
LinkedList<int> l;
l.append(10);
}
Other comments:
this.val won't compile, because this is a pointer. You meant this->val.
You should consider using member initializer lists instead of this->val = val.
Initialize all members in all constructors.