Thread: Problem with creating a singly linked list

I was carefully going through the examples in a book of mine. Everything was going fine until I created the SListIterator class. It keeps pointing at its constructor. I tried everything but no luck. Here are the errors:

error C2143: syntax error : missing ';' before '<'
error C2501: 'X3D::SListIterator<Datatype>::SLinkedList' : missing storage-class or type specifiers
error C2238: unexpected token(s) preceding ';'
error C2143: syntax error : missing ')' before '<'
error C2143: syntax error : missing ';' before '<'
error C2059: syntax error : ')'
error C2334: unexpected token(s) preceding '{'; skipping apparent function body

Any help would be appreciated. Thanks.

SListNode.h:

Code:

#ifndef SLISTNODE_H
#define SLISTNODE_H

namespace X3D
{
	template <typename Datatype> class SListNode
	{
	public:
		Datatype m_data;
		SListNode<Datatype> *m_next;

		// Inserts a new data value in the linked list. This is 
		// not sorted nor put at the very end of the list. 
		void InsertAfter(Datatype data)
		{
			// create the new node and assign its given value.
			SListNode<Datatype> *newNode = new SListNode<Datatype>;
			newNode->m_data = data;
            // have the new node point to the next node. 
			newNode->m_next = m_next;
			// make the previous node point to the new node. 
			m_next = newNode;
		}
	};
}

#endif

SLinkedList.h:

Code:

#ifndef SLINKEDLIST_H
#define SLINKEDLIST_H

#include "SListNode.h" 
#include "SListIterator.h"

namespace X3D
{
	template <typename Datatype> class SLinkedList
	{
	public:
		SListNode<Datatype> *m_head;
		SListNode<Datatype> *m_tail;
		int m_count;

		SLinkedList()
		{
			m_head = 0;
			m_tail = 0;
			m_count = 0;
		} 

		~SLinkedList()
		{
			SListNode<Datatype> *itr = m_head;
			SListNode<Datatype> *next;

			while (itr != 0) 
			{
				// save the pointer to the next node
				next = itr->m_next;
				// delete the current node
				delete itr;
				// make the next node the current node
				itr = next;
			}
		}

		void Append(Datatype data)
		{
			if (m_head == 0) 
			{
				m_head = m_tail = new SListNode<Datatype>;
				m_head->m_data = data;
			}
			else 
			{
				// insert a new node after the tail and reset the tail.
				m_tail->InsertAfter(data);
				m_tail = m_tail->m_next;
			}

			m_count++;
		}

		// adds a new node at the beginning of the list. 
		void Prepend(Datatype data)
		{
			// create a new node
			SListNode<Datatype> *newNode = new SListNode<Datatype>;
			newNode->m_data = data;
			newNode->m_next = m_head;
			// set the head node and the tail node if needed. 
			m_head = newNode;
			if (m_tail == 0) 
				m_tail = m_head;
			m_count++;
		}

		void RemoveHead()
		{
			SListNode<Datatype> *node = 0;

			if (m_head != 0) 
			{
				node = m_head->m_next;
				delete m_head;
				m_head = node;

				if (m_head == 0)
					m_tail = 0;

				m_count--;
			}
		} 

		void RemoveTail()
		{
			SListNode<Datatype> *node = m_head;

			while (m_head != 0)
			{
				if (m_head == m_tail) 
				{
					delete m_head;
					m_head = m_tail = 0;
				}
				else 
				{
					while (node->m_next != m_tail) 
						node = node->next; 
				
					m_tail = node;
					delete node->m_next;
					node->m_next = 0;
				}

				m_count--;
			}
		}

		// Creates a new iterator pointing to the head in the 
		// current list. 
		SListIterator<Datatype> GetIterator()
		{
			return (SListIterator<Datatype>(this, m_head));
		}
	};
}

#endif

SListIterator.h:

Code:

#ifndef SLISTITERATOR_H
#define SLISTITERATOR_H

#include "SLinkedList.h"

namespace X3D
{
	template <typename Datatype> class SListIterator
	{
	public:
		SListNode<Datatype> *m_node;
		SLinkedList<Datatype> *m_list;

		// Initializes the iterator. 
		SListIterator(SLinkedList<Datatype> *list = 0, 
			SListNode<Datatype> *node = 0)
		{
			m_list = list;
			m_node = node;
		}

		// Resets the iterator to the head node of the list.
		void Start()
		{
			if (m_list != 0)  
				m_node = m_list->m_head; 
		} 

		// Moves the iterator towards the next node in the list. 
		void Forth()
		{
			if (m_list != 0) 
				m_node = m_node->m_next;
		}

		// Returns a reference of the item stored in the node
		// that the iterator is pointing to.
		Datatype& Item()
		{
            return (m_node->m_data);
		}

		// Returns true if the current node being pointed to is 
		// valid. Returns false otherwise.
		bool Valid()
		{
			return (m_node != 0);
		}
	};
}

#endif

Looks like you have a recursive include. Perhaps one of those should be a forward declaration.

Each class is in its own header file. I wonder if it's just the wrong includes on top? The syntax looks fine, so if its just having a problem with SListIterator, it seems that its not the code but the includes somehow.

Yes, you have a recursive include. That means that one header includes another, and that header includes the first. That won't work, because the source file can only include one of them first.

Do you know what a forward declaration is? You have to change one of the header files to not include the other, but instead use a forward declaration of some sort.

Okay, thanks for letting me know.

Since you added the forward declaration, you can easily separate them into separate files if you'd like to do that. In this case I would think either way is fine.