Re: Polymorphism?

From:
=?Utf-8?B?Um9iYnk=?= <Robby@discussions.microsoft.com>
Newsgroups:
microsoft.public.vc.language
Date:
Sat, 13 May 2006 09:38:01 -0700
Message-ID:
<57B9008B-7415-4288-8A40-0F3881F01E2C@microsoft.com>
Hi Ian...

Thankyou for replying!

well here is the code with the implentations, however no luck I still get
the same 2 errors....
===================================================

//==//ADT BASE CLASS
class components
{
public:
components();
virtual ~components() {}
virtual void ACommonMethod()= 0;

private:
int a;
};

void components::ACommonMethod()
{
a = 10;
}

//ADT
class actions:public components
{
public:
actions();
virtual ~actions(){}
};

class A_SETV:public actions
{
public:
A_SETV();
virtual ~A_SETV(){}
virtual void ACommonMethod();
virtual void InnitStep();
protected:
int zzz;
};

void A_SETV::ACommonMethod()
{
components::ACommonMethod();
}

void A_SETV::InnitStep()
{
zzz = 20;
}
=====================================================

I don't know what else to try... I don't have much experience with creating
classes with inheritance and polymorphsim!

Do you have any other idea of what can be generating these errors....?
or let me know if I made a mistake in my code this time around!

Your help is much appreciated in getting me over this hurdle!

Thankyou very much!

--
Best regards
Robert

"Ian" wrote:

"Robby" <Robby@discussions.microsoft.com> wrote in message
news:565FC2E2-80B3-41AA-A79C-FB8CE1657663@microsoft.com...

Hello,

I though I had understood the concept of inheritance, poymorphism and
ADT's... but I guess there is still some minor details that escape me.

Please consider the following code:
==================================================
//ADT BASE CLASS
class components
{
public:
components();
virtual ~components();
virtual void ACommonMethod()= 0;

protected:
};

//ADT
class actions:public components
{
public:
actions();
virtual ~actions();
};

class A_SETV:public actions
{
public:
A_SETV();
virtual ~A_SETV();
virtual void ACommonMethod();
virtual void InnitStep();
protected:
};

//Instantiate a A_SETV object so I can fetch its methods
components *pA_SETV = new A_SETV;

//Fetch A_SETV method
pA_SETV->ACommonMethod();

delete pSetV;

==================================================

The following code fragment gives me the following errors:

WndProc.obj : error LNK2019: unresolved external symbol "public:
__thiscall
A_SETV::A_SETV(void)" (??0A_SETV@@QAE@XZ) referenced in function "long
__stdcall WndProc(struct HWND__ *,unsigned int,unsigned int,long)"
(?WndProc@@YGJPAUHWND__@@IIJ@Z)

Debug/MT_3.exe : fatal error LNK1120: 1 unresolved externals

I don't know what I am doing wrong.. I have declared a simple ADT
(abstract
data type) called 'components' and made another class derive from the base
class called 'actions' which is another ADT. The reason why I beleive that
actions is an ADT is because it does not overide the pure virtual function
in
the base class...right!

Then I derived another class from actions called A_SETV and I was trying
to
fetch a common method in the base class by doing:

components *pA_SETV = new A_SETV;
pA_SETV->ACommonMethod();

I also tried to fetch a method in the A_SETV class as so:

A_SETV *pA_SETV = new A_SETV;
pA_SETV->virtual void InnitStep();

In either case I always get the errors stipulated above....

PS... and the best part of all this, is that, last night, this program
compile withou any errors..... confused, I ask my self, what's going on!

Can someone help....

All suggestions a very appreciated!

Thankyou all!

--
Best regards
Robert


it compiles OK, it doesn't link because you haven't provided the
implementation

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