Pointer to a Struct/ Class within the struct/class C++ - c++

Question

Hi I am from a Java background and quite new to C++
In my intermediate level of Java programming i never had situation where i declared an object of some
class within the body of that class, now am studying linked lists in C++, here in this code and in several
other places i have come across that pointer to that class/struct is declared within its body i.e Struct ListNode * next; in the following code
private:
// Declare a structure for the list
structListNode{
float value;
structListNode*next;
};
ListNode*head; // List head pointer
public:
FloatList(void) { // Constructor
head = NULL;
}
~FloatList(void) { }; // Destructor
void appendNode(float);
void displayList(void);
void deleteNode(float);
};
or Node * next ; in this code below
class Node {
int data; // The value stored in node
Node* next; // The address of next node
}
I can'really comprehend what it means or how is it going , can someone please explain it to me?

Answer 1

The pointer inside struct/class is not an "object" of that struct/class, instead, it is a pointer of the objects of the same type. It just stores/holds address of objects created somewhere else, so it can access or modify them without copying their content.
As an example;
class Node {
int data;
Node* next;
};
int main(){
Node* head = NULL; // This is a pointer, not an object.
// It points to NULL (i.e. nothing) yet.
Node n1, n2; // These two are "objects" of Node class
head = &n1; // head now points to n1, i.e. holds memory address of n1
n1.data = 10; // n1.data contains 10
n1.next = &n2; // n1.next points to the object n2
n2.data = 20; // n2.data contains 20
n2.next = NULL; // n2.next points to nothing
head->data = 5; // now, n1.data contains 5, instead of 10
head->next->data = 15; // now, n2.data contains 15, instead of 20
return 0;
}