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missing storage-class or type specifiers

Posted on 2004-09-09
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Last Modified: 2010-04-01
I created a header file including a Node Class and a
NodeList.

class Node{
  Node* next;
};

class NodeList{
 Node* first;
 Node* last;
};

I wanna declare a NodeList inside the Node but since
NodeList is declared after Node it's impossible!!!
like this...

class Node{
  Node* next;
  NodeList list;
};

I get:
error C2146: syntax error : missing ';' before identifier 'list'
error C2501: 'Node::list' : missing storage-class or type specifiers
error C2501: 'Node::NodeList' : missing storage-class or type specifiers

What do you do in such cases? I am familiar with Java but it seems that C++ is very capricious and does not allow this kind of things.

Help me plz...30 points is all I got :)
0
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Question by:Trooper80
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4 Comments
 
LVL 12

Accepted Solution

by:
stefan73 earned 30 total points
ID: 12016410
Hi Trooper80,
Use a forward declaration:

class Node;

class NodeList{
 Node* first;
 Node* last;
};


class Node{
  Node* next;
  NodeList list;
};

You can only use pointers to classes not yet defined. Probably you wanted to have
class Node{
  Node* next;
  NodeList* list;
};


Cheers!

Stefan
0
 
LVL 39

Expert Comment

by:itsmeandnobodyelse
ID: 12017772
>>>> I wanna declare a NodeList inside the Node

That makes no sense. A Node only has pointers to other Nodes. If you want to go backwards you should have a 'prev' pointer:

class Node
{
    Node* next;
    Node* prev;  // to iterate backwards
};

If you want to implement a tree, you may have that:

class Node
{
    Node* parent;   // to go up
    Node* left;       // to go left
    Node* right;     // to go right
    Node* first;      // to go down-left
    Node* last;       // to go down-right

public:
    Node() : parent(NULL), left(NULL), right(NULL), first(NULL), last(NULL) {}
};

Regards, Alex

0
 
LVL 1

Author Comment

by:Trooper80
ID: 12019228
Hey Alex thanks for the tip man but I know what I'm doing. Everynode will have a sub-set of nodes connected to it...so why not use a linked list again but this itme with only the nodes that are connected to it?
0
 
LVL 39

Expert Comment

by:itsmeandnobodyelse
ID: 12019390
>> why not use a linked list

The class NodeList from above actually isn't a list, but has only two Node pointers, first and last. 'last' doesn't help as long as you have no 'prev' pointer in class Node and having only a 'first' pointer makes no sense as you could have the  'first' Node pointer in class Node instead of a NodeList (or NodeList pointer) with less overhead.

But, if you think you need that NodeList class, do it the way Stefan told you: Have a forward declaration of class Node, then define class NodeList using Node pointers (as they are only declared but not defined). Then, you can define class Node using either a NodeList pointer or a NodeList object as data member:

class Node;

class NodeList
{
     Node* first;
     Node* last;

public:
    NodeList() : first(NULL), last(NULL) {}
};

class Node
{
    Node*    next;
    Node*    prev;  // to iterate backwards
    NodeList list;

public:
    Node() : next(NULL), prev(NULL) {}
};

Regards, Alex

0

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