first c++ mini-project. an issue

Asido · 12-29-2010, 09:31 AM

Hello guys.

I am trying to write my first small project with C++ - implement stl list like collection class. This is what i have a the moment:

Code:

#ifndef GUARD_link_list_h

#define GUARD_link_list_h

template <class T>
struct Node {
	public:
		Node() { link = NULL; }
		Node(const Node* l, const T& d) { link = l; data = d; }

		T& get_data() { return data; }
		void set_data(const T& v) { data = v; }
		Node* get_link() { return link; }
		void set_link(Node* l) { link = l; }

	private:
		Node* link;
		T data;
};

template <class T>
class Link_list {
public:
	typedef T* iterator;
	typedef const T* const_iterator;
	typedef T value_type;
	typedef size_t size_type;

	// The Rule of Three
	Link_list () { init(); }
	virtual ~Link_list () {}
	//Link_list& operator=(const Link_list&);

	// operators
	T* operator++() { return next(); }

	// methods to manage the collection
	void push_back(const T&);
	iterator begin() { return first; }
	iterator end() { return last; }
	bool empty() { return first == 0; }

private:
	Node<T>* node;
	iterator first;
	iterator last;
	
	// private methods
	void init();
	T* next();
};

template <class T>
void Link_list<T>::init() {
	first = last = 0;
}

template <class T>
void Link_list<T>::push_back(const T& v) {
	Node<T> *n = new Node<T>;
	n->set_data(v);
	n->set_link(node);
	node = n;
	if(!empty())
		last = &(node->get_data());
	else
		first = last = &(node->get_data());
}

template <class T>
T* Link_list<T>::next() {
	node = node.get_link();
	return node.get_data();
}

#endif /* end of include guard: GUARD_link_list_h */

I know it's not a very nice code.
The issue I have is with data values. I test it with this code:

Code:

Link_list<int> t;
	t.push_back(5);
	t.push_back(9);
	t.push_back(2);

	Link_list<int>::iterator it = t.begin();
	std::cout << *it << std::endl;
	++it;
	std::cout << *it << std::endl;

	Link_list<int>::iterator it2 = t.end();
	std::cout << *it << std::endl;

The begin() and end() is alright, but the problem is when I try to increment the iterator. The value is 0, while I expect 9.
What did I do wrong here (presumably with pointers)?
Also, some comments on coding style would be nice about bad C++ programming practice you might notice here.

johnsfine · 12-29-2010, 09:46 AM

Quote:

Originally Posted by Asido

typedef T* iterator;

That means a Link_list::iterator is exactly a T* and acts in all ways as a T*. You can't redefine any of the operation of Link_list::iterator.

Quote:

T* operator++() { return next(); }

That is an operator on Link_list, not on Link_list::iterator.

Quote:

Also, some comments on coding style would be nice about bad C++ programming practice you might notice here.

Code:

        Node() { link = NULL; }
        Node(const Node* l, const T& d) { link = l; data = d; }

NULL is bad style for C++, just use 0.
Too much one one line is bad style.
Assignments inside the constructor body are bad style for member initialization in C++. Use the special syntax for member initialization:

Code:

        Node() :
           link( 0 )
        {}
        Node(const Node* l, const T& d) :
           link( l ),
           data( d )
        {}