Compile-time error: expected constructor, destructor or conversion

I need some help

does this piece of 开发者_C百科code look right ?

#include "programass.h"

#include <cstdlib>
#include <iostream>
#include <string>
#include "Student.h"
using namespace std;

template<class emptyValue>

struct DoublyLinkedNode
{
    emptyValue data;
    DoublyLinkedNode *prev, *next;
};
typedef DoublyLinkedNode<int> numListNode;
DoublyLinkedNode *listHead = NULL;
DoublyLinkedNode *listTail = NULL;

I keep getting a " expected constructor, destructor or conversion before "*" " error in debugger ? on the last two lines what have i done wrong ? :(

---

You did

typedef DoublyLinkedNode<int> numListNode;

but in the next two lines

DoublyLinkedNode *listHead = NULL;
DoublyLinkedNode *listTail = NULL;

you forgot to use that new numListNode type. Change them to

numListNode *listHead = NULL;
numListNode *listTail = NULL;

Because you can't use a template class without a template argument, and you tried to do DoublyLinkedNode *listHead when it should have been DoublyLinkedNode<something> *listHead. So if you use your typedef which specifies the template argument (as int), it works.

---

I am sure you wanted to use numListNode instead of DoublyLinkedNode at the declaration of the two pointers.

numListNode* listHead = NULL;
numListNode* listTail = NULL;

On a side note I recommend removing the blank line between template <class emptyValue> and struct DoublyLinkedNode, and using the style Type* ptr; instead of Type *ptr;, it's nicer that way.

---

Seth is right, but if I understand correctly, you're trying to build a generic data type, and hence want to have list head and tail also templated. For that you need a container struct that will also hold them:

template < typename emptyValue >
struct List 
{
    struct DoublyLinkedNode
    {
        emptyValue data;
        DoublyLinkedNode *prev, *next;
    };
    DoublyLinkedNode *head;
    DoublyLinkedNode *tail;

    ....
}

typedef List<int> numList;