dynamic object creation

[Vinhuard]

Hi Gurus!

I need your help on this one...

I got a wizard...the user is selecting wich program he want to convert his address book from...I've made several object that got the same function to be call...

so, depend on the selection the user has made...I want to create my addrbook object and after use it..because the function are all the same for each objet...I don,t want to write 8 time the same code....so i've proceed with a switch as you can see with this sample of code...

But....my addrbook object is no longer valide when I get out of the switch and want to use it..what can I do ???

thanks a lot!!

ViNcE...

P.S. sorry for my bad english...speaking french





switch(iChoix)
{
case 0:
CNSv2v3 addrBook;
break;
case 1:
CNSv4 addrBook;
break;
case 2:
CNSv6 addrBook;
break;
case 3:
COutExp addrBook;
break;
case 4:
CLDIF addrBook;
break;
case 5:
CCSV addrBook;
break;
case 6:
COut979820002002 addrBook;
break;
case 7:
CTabText addrBook;
break;
case 8:
CMSExchange addrBook;
break;
}


//Création du contact.
CONTACT contact;

addrBook.GetContact(1,&contact);

[DanielK]

The reason this happens is because the object is created on the stack. This is ok, until you go out of scope: A variable declared in a function is destroyed when the function is over, a variable declared inside an if is destroyed at the end of the if block, and a variable declared inside a switch case block is also destroyed when the switch block is closed. You can solve this be using a pointer to an object(declared outside the switch, and a call to new to allocate the object inside the switch).

Got a question? try looking it up in MSDN first. Msdn comes with the Visual Studio, and can be found at http://msdn.microsoft.com
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I'm not here for the rates, but rating a post is a good way for me to know how much i helped.
---===---
Daniel

[Kevin Cook]

with the assumption that all of your classes derive from a common class you can do the following:


CMyAddressBookInterface *pInterface;

switch(iChoix)
{
case 0:
pInterface = new CNSv2v3;
break;
case 1:
pInterface = new CNSv4;
break;
//other cases follow
}

CONTACT aContact;
pInterface->getContact(1, &aContact);
delete pInterface;




Of course all the other considerations must apply about scoping rules etc.

--------------------------------------------------------------------------------------
Its really a simple problem, once you've worked it out.

[Vinhuard]

I knew about the stack thing...I just don't know how to solve my problem.

ok yeah....this is what I was thinking....but

because I got different type of objet...

so....what is my pointer declaration ?

I can't declar my pointer like this :

CNSv4 * addrBook = NULL;



and after in my switch using it like this no ?

addrBook = new COutExp;



can I do this???

thanks!

[Vinhuard]

thanks...ok hmmm

If I understand things right....
CMyAddressBookInterface is the base class..

It contain virtual functions....

and I only wrote code into my derived class..CNSv4...CNSv2v3 and etc....

is it that ?

thanks!

[DanielK]

In reply to:


If I understand things right....




it doesn't get righter than that!

Got a question? try looking it up in MSDN first. Msdn comes with the Visual Studio, and can be found at http://msdn.microsoft.com
---===---
I'm not here for the rates, but rating a post is a good way for me to know how much i helped.
---===---
Daniel

[Kevin Cook]

Yeah, something like this:


class CONTACT; //forward declare the contact type
class CMyAddressBookInterface
{
public:
virtual void getContact(int nIndex, CONTACT *pContact) = 0;
};


class CONTACT; //forward declare the contact type
class CNSv4 : public CMyAddressBookInterface
{
virtual void getContact(int nIndex, CONTACT *pContact)
{
//this example has this method inline, but the method doesn't HAVE to be inlined
}
};




--------------------------------------------------------------------------------------
Its really a simple problem, once you've worked it out.

[Vinhuard]

last question ;-)

can my private member like int iNbContact;

be declare into the base class.. ?

If yes....do I have to put virtual before the declaration ?

thanks...

my knowledge is not very big around virtual things

ViNcE

[Kevin Cook]

It can be, but I prefer to use interfaces as just interfaces...therefore they have no data members. One of the things that you'll have to consider if you do add the data variable as a private member of your base interface class is that you'll want a constructor to initialize the variable. Its all a matter of your style, and it can certainly be done.

--------------------------------------------------------------------------------------
Its really a simple problem, once you've worked it out.