pointer1 = pointer1 ->pointer2 syntax

[Deliberation]

Hi everyone,

I need help on why following program brings an error message.
Whenever arrow() is accessed by Object, it shows an error message EXC_BAD_ACCESS, and really don't know the meaning of the code
other1 = other1->other2. The reason why I made this program is that I was curious of how current = current->next was interpreted in the line number 96 of the second program below.

#include <iostream>
using namespace std;

struct foo{
    int x;
    foo *other1;
    foo *other2;
    void arrow(){
        other1 = other1->other2;
    }
    
};

int main(){
    foo Object;
    Object.arrow();
    
    cout << Object.other1 <<endl;
    cout << Object.other2<<endl;
   
    return 0;
}

#ifndef LIST_H // // multiple inclusion guard
#define LIST_H

template <typename Object>
class List
{
private:
	struct Node // private member structure (could be class instead)
	{
		Object data;
		Node* prev;
		Node* next;
		Node(const Object& d = Object(), Node* p = NULL, Node* n = NULL) // constructor
			: data(d), prev(p), next(n) {}
		Node(Object&& d, Node* p = NULL, Node* n = NULL) // move constructor (C++11)
			: data(move(d)), prev(p), next(n) {}
	};

public:
	class const_iterator // **********************************************
	{
	public:
		const_iterator() : current(NULL) {} // default constructor

		const Object& operator*() const // const de-referencing
		{
			return retrieve();
		}

		const_iterator& operator++() // pre-increment
		{
			current = current->next;
			return *this;
		}

		const_iterator operator++(int) // post-increment
		{
			const_iterator old = *this;
			++(*this);
			return old;
		}

		const_iterator& operator--() // pre-decrement
		{
			current = current->prev;
			return *this;
		}

		const_iterator operator--(int) // post-decrement
		{
			const_iterator old = *this;
			--(*this);
			return old;
		}

		bool operator== (const const_iterator& rhs) const
		{
			return current == rhs.current;
		}

		bool operator != (const const_iterator& rhs) const
		{
			return !(*this == rhs);
		}

	protected:
		Node* current;

		Object& retrieve() const
		{
			return current->data;
		}

		const_iterator(Node* p) : current(p) {} // constructor

		friend class List<Object>;
	}; // end class const_iterator // **********************************************

	class iterator : public const_iterator // **************************************
	{
	public:
		iterator() : current(NULL) {} // default constructor

		Object& operator*() // de-referencing
		{
			return retrieve();
		}

		const Object& operator*() const // const de-referencing
		{
			return const_iterator::operator*();
		}

		iterator& operator++() // pre-increment
		{
			current = current->next;
			return *this;
		}

		iterator operator++(int) // post-increment
		{
			iterator old = *this;
			++(*this);
			return old;
		}

		iterator& operator--() // pre-decrement
		{
			current = current->prev;
			return *this;
		}

		iterator operator--(int) // post-decrement
		{
			iterator old = *this;
			--(*this);
			return old;
		}

	private: // we are not expecting to derive from iterator...
		iterator(Node* p) : const_iterator(p) {} // constructor

		friend class List<Object>;
	};// end class iterator // **********************************************

	// back to class List:
public:
	// constructors
	List() // default
	{
		init();
	}

	List(const List& rhs) // copy constructor
	{
		init();
		for (const Object& x : rhs) // range-based for loop (C++11)
			push_back(x);
	}

	List(List&& rhs) // move constructor (C++11)
		: theSize(rhs.theSize), head(rhs.head), tail(rhs.tail)
	{
		rhs.theSize = 0;
		rhs.head = NULL;
		rhs.tail = NULL;
	}

	// destructor
	~List()
	{
		clear();
		delete head;
		head = NULL;
		delete tail;
		tail = NULL;
	}

	// public assignment operator
	List& operator=(const List& rhs)
	{
		if (this != &rhs) // prevent assignment to itself
		{
			this->clear();
			for (const_iterator itr = rhs.begin(); itr != rhs.end(); ++itr)
				this->push_back(*itr);
		}
		return *this;
	}

	iterator begin()
	{
		return iterator(head->next);
	}

	const_iterator begin() const
	{
		return const_iterator(head->next);
	}

	iterator end()
	{
		return iterator(tail);
	}

	const_iterator end() const
	{
		return const_iterator(tail);
	}

	size_t size() const
	{
		return theSize;
	}

	bool empty() const
	{
		return size() == 0;
	}

	void clear()
	{
		while (!empty())
			pop_front();
	}

	Object& front()
	{
		return *begin();
	}

	const Object& front() const
	{
		return *begin();
	}

	Object& back()
	{
		return *--end();
	}

	const Object& back() const
	{
		return *--end();
	}

	void push_front(const Object& x)
	{
		insert(begin(), x);
	}

	void push_back(const Object& x)
	{
		insert(end(), x);
	}

	void pop_front()
	{
		erase(begin());
	}

	void pop_back()
	{
		erase(--end());
	}

	// Insert copy of x on the free store before itr:
	iterator insert(iterator itr, const Object& x)
	{
		Node* p = itr.current;
		theSize++;
		try
		{
			// new Node allocated on the freestore
			p->prev = p->prev->next = new Node(x, p->prev, p);
		}
		// if memory allocation failed:
		catch (...) // executes in case of exception (error)
		{
			cout << "Error encountered... quitting, sorry!\n";
			system("pause");
			exit(EXIT_FAILURE); // quit
		}
		return iterator(p->prev);
	}

	// Erase item at itr:
	iterator erase(iterator itr)
	{
		if (!empty())
		{
			Node* p = itr.current;
			iterator retVal(p->next);
			p->prev->next = p->next;
			p->next->prev = p->prev;
			delete p;
			p = NULL;
			theSize--;
			return retVal;
		}
		else
		{
			cout << "List empty!\n";
			return NULL;
		}
	}

	// Erase items from start to end:
	iterator erase(iterator start, iterator end)
	{
		for (iterator itr = start; itr != end;)
			itr = erase(itr);
		return end;
	}

private:
	size_t theSize;
	Node* head;
	Node* tail;

	void init()
	{
		theSize = 0;
		try
		{
			head = new Node; // on the free store
			tail = new Node; // on the free store
		}
		// if memory allocation failed:
		catch (...) // executes in case of exception (error)
		{
			cout << "Error encountered... quitting, sorry!\n";
			system("pause");
			exit(EXIT_FAILURE); // quit
		}
		head->next = tail;
		tail->prev = head;
	}
};// end class List

#endif

[DyslexicChciken]

A pointer is a variable that points to an address in memory. You can also make pointers to objects that contain methods and data. Each pointer can only point to the type of object defined as the type of the pointer.

node<int> * node_pointer;

Above is a pointer to a node that contains int data, and only a node that contains int data.

 node_pointer = new node<int>(10);

Above initializes our node pointer to point to a node that contains 10. What happens if we want to get 10 from the node_pointer?

Normally if node_pointer wasn't a pointer, we would do this:

int element = node_pointer.getElement();

But because node_pointer is a pointer to the object and not the object itself, we need to use the arrow notation to get the element:

int element = node_pointer->getElement();

The code above is equivalent to:

int element = (*node_pointer).getElement();

The code above dereferences node_pointer (using '*' operator) and calls the method, getElement(), of the object pointed to by node_pointer. This returns the element 10.

However if instead of getElement() we have getNextPointer(), then it would look like this:

node<int> * new_pointer = node_pointer->getNextPointer();

node_pointer invokes getNextPointer() which returns a pointer to the next node in a linked list and assigns it to another node pointer type called new_pointer.