Factory method in Interface

[DBarzo]

Hi,

I have an abstract class which defines an interface for an object.
Now I need a factory method to create object.

IMyObj.h

public class IMyObj
{
  virtual int Method1() = 0;
  static IMyObj* CreateMyObj();
}

CMyObj.h

#include "IMyObj.h"

public class CMyObj : public IMyObj
{
  int Method1();
  static IMyObj* CreateMyObj();
}

CMyObj.cpp

#include "CMyObj.h"

int CMyObj::Method1() 
{ ... }

IMyObj* CreateMyObj() 
{ return new MyObj(); }

When I use the code in a test project I receive "unresolved external symbol" on IMyObj::CreateMyObj

#include "IMyObj.h"

IMyObj* pMyObj = IMyObj::CreateMyObj();

Where I wrong?

Regards,
Daniele.

[kbw]

Your syntax is incorrect.

IMyObj.j should have:

class IMyObj
{
public:
  virtual int Method1() = 0;
  static IMyObj* CreateMyObj();
};

... and so on.

[DBarzo]

Yes, sorry...I forgot the 'public' keywork in the example...but, of course, in my code I put it!
Daniele.

[kbw]

It all depends on where you want the creator to go. But let's assume that you want one in each concrete class and not the interface, then CMyObj.cpp should be:

#include "CMyObj.h"

int CMyObj::Method1() 
{ ... }

IMyObj* CMyObj::CreateMyObj() 
{ return new MyObj(); }

IMyObj.h should have:

class IMyObj
{
public:
  virtual int Method1() = 0;
};

And CMyObj.h remains unchanged.