classes as member variables

Hi,

I don't have a lot of time atm, so I'll save you the usual verbose intro of how I got myself in my current predicament :P

Basically I have a header file, looks something like this

Code:

---

#ifndef CLASSES_H
#define CLASSES_H

#include <iostream>
using namespace std;


//******* Part **************

//Abstract class of parts
class Part
{
        public:
                Part():itsPartNumber(1){}
                Part(int num):itsPartNumber(num){}
                virtual ~Part(){};

                int getPartNumber(){ return itsPartNumber; }
                virtual void Display() const = 0; //must be overidden

        private:
                int itsPartNumber;
};

//some other derived classes, ommited to save space

//********** Part Node *************

class PartNode
{
        public:
                PartNode(*Part);
                ~PartNode();

                void setNext(PartNode * node){ itsNext = node; }

                PartNode * getNext() const;
                Part* getPart() const;

        private:
                Part* itsPart;
                PartNode * itsNext;

};

#endif

---

I have another .cpp file which "includes" this header and simply implements the pure virtual function in the abstract class. I also have a main.cpp file which contains the driver (main) function.

When I try to compile I get the following.

Code:

---

error C2327: 'PartNode::Part' : is not a type name, static, or enumerator

---

I get it a couple of times, once for the function which returns a pointer to a Part, and the other time when I declare one of the member variables of the node class to be a pointer to a Part.

They are the only errors I'm getting.

I think I'm making some fundamental error when it comes to having classes as member variables of other classes, but I don't know what it is. Any help would be much appreciated, thanks :)

Regards,

Stonehambey

Perhaps PartNode(*Part) should be: PartNode(Part*)

Oh yes, and do not use using directives in header files except within some restricted scope.

Quote:

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Originally Posted by laserlight

Perhaps PartNode(*Part) should be: PartNode(Part*)

Oh yes, and do not use using directives in header files except within some restricted scope.

---

Interesting, that solves the problem...but I don't know why :(

*Part dereferences some pointer named Part, but Part is a class name, not a pointer. Part* is the type of a pointer to a Part object.

ok, I see my error there.

Why was the compiler specifically flagging these two lines though?

Code:

---

Part* getPart() const;

...

Part* itsPart;

---

When the error was in the PartNode constructor.

Quote:

---

Why was the compiler specifically flagging these two lines though?

---

Unfortunately, I do not know. Part seems to play the part of a type name in those two lines.

Maybe the fault is in the constuctor of PartNode ...
Also you should define a standard constuctor for every class.


Greetz

BTW, you should never put using statements inside a header file or before an #include statement; otherwise it could change the meaning of your code. i.e. Don't put this in your header files:

Code:

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using namespace std;

---

>> Also you should define a standard constuctor for every class.
I disagree with this advice. You should only define a standard constructor when you need it, and often you don't. If you leave it out you help enforce proper use of your class.

What is a standard constructor? A default constructor?

>> What is a standard constructor? A default constructor?
I don't know, that's what I assumed and what I was commenting on.

Quote:

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Originally Posted by laserlight

What is a standard constructor? A default constructor?

---

Yes, I ment the default constructor, sorry, I'm german ... :D

EDIT:

Quote:

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I disagree with this advice. You should only define a standard constructor when you need it, and often you don't. If you leave it out you help enforce proper use of your class.

---

But related to the code above, this declaration will produce an error

Code:

---

PartNode pn1;    // Error

---

, doesn't it ?


Greetz

Hi, thanks for the replies everyone :)

I compile as I go along, which I have found allows me to catch and locate errors quicker. In this case the error occurred before I had time to define the default constructor for the PartNode class, (which, ironically, was the source of the error :P)

Sorry about using namespace std. This program was to play a bit with abstract classes and virtual member functions, which I've just learned about, so I was feeling a bit lazy, although I realise that's no excuse to pick up bad habits! :P

Ciao

Stonehambey

>> But related to the code above, this declaration will produce an error
>> PartNode pn1; // Error

Yes, it would, but I don't see that code anywhere. In fact, one reason to not specify the default constructor is so that the code would produce an error because that's not how you're supposed to use that class.

Whether this particular class needs a default constructor or not I do not know, but in general you should only add one if it is necessary.