Need clarification about virtual methods & inheritance

[mark]

I have this class:
class Selections {
OSStatus Init();

protected:
CFMutableSetRef selectionObject s;
static void CFASelectionsAp plier(const void* value, void* ctx);
OSType ready;
public:
Selections();
Selections(cons t Selections &obj);
virtual ~Selections();

virtual OSType GetSelectionSco pe();

virtual UInt32 GetSelectCount( SelectionFlag whichFlags);
virtual CFArrayRef GetSelObjects(S electionFlag whichFlags);
UInt32 GetCountOfClass (SelObjectClass theClass);
CFArrayRef GetSelObjectsOf Class(SelObject Class theClass);
virtual UInt32 GetCountOfScope (OSType theScope);
virtual CFArrayRef GetArrayofScope (OSType theScope);

virtual OSStatus MassAddSelObjec ts(CFArrayRef sorArray);
virtual OSStatus AddSelectededOb ject(SelectedOb jectRef soref);
virtual OSStatus MassRemoveSelOb jects(CFArrayRe f sorArray);
virtual OSStatus RemoveSelectedO bject(SelectedO bjectRef soref);
virtual void RemoveAllSelect edObjects(Selec tionFlag whichFlags);
void RemoveSelObject sOfClass(SelObj ectClass theClass);
virtual void RemoveSelObject sOfScope(OSType theScope);
virtual void RemoveAll();
};

and a subclass:

typedef class DirView DirView;

class DVSelections: public Selections {
DirView* view;
OSType dvsReady;
public:
DVSelections(Di rView* theView);
DVSelections(co nst DVSelections &obj);
~DVSelections() ;

OSType GetSelectionSco pe();
DirView* GetView();
};

When I attempt to compile it, the linker complains with this message:
/usr/bin/ld: Undefined symbols:
vtable for DVSelections

I was under the impression if the virtual function is not defined in a
subclass, the parent class's function will be used.
What am I missing?

This is mac OS X, XCode 2.2 with gcc 4.

TIA
Mark

[Victor Bazarov]

mark wrote:

I have this class:
class Selections {
OSStatus Init();

protected:
CFMutableSetRef selectionObject s;
static void CFASelectionsAp plier(const void* value, void* ctx);
OSType ready;
public:
Selections();
Selections(cons t Selections &obj);
virtual ~Selections();

virtual OSType GetSelectionSco pe();

virtual UInt32 GetSelectCount( SelectionFlag whichFlags);
virtual CFArrayRef GetSelObjects(S electionFlag whichFlags);
UInt32 GetCountOfClass (SelObjectClass theClass);
CFArrayRef GetSelObjectsOf Class(SelObject Class theClass);
virtual UInt32 GetCountOfScope (OSType theScope);
virtual CFArrayRef GetArrayofScope (OSType theScope);

virtual OSStatus MassAddSelObjec ts(CFArrayRef sorArray);
virtual OSStatus AddSelectededOb ject(SelectedOb jectRef soref);
virtual OSStatus MassRemoveSelOb jects(CFArrayRe f sorArray);
virtual OSStatus RemoveSelectedO bject(SelectedO bjectRef soref);
virtual void RemoveAllSelect edObjects(Selec tionFlag whichFlags);
void RemoveSelObject sOfClass(SelObj ectClass theClass);
virtual void RemoveSelObject sOfScope(OSType theScope);
virtual void RemoveAll();
};

and a subclass:

typedef class DirView DirView;

class DVSelections: public Selections {
DirView* view;
OSType dvsReady;
public:
DVSelections(Di rView* theView);
DVSelections(co nst DVSelections &obj);
~DVSelections() ;

OSType GetSelectionSco pe();
DirView* GetView();
};

When I attempt to compile it, the linker complains with this message:
/usr/bin/ld: Undefined symbols:
vtable for DVSelections

I was under the impression if the virtual function is not defined in a
subclass, the parent class's function will be used.
What am I missing?

Could it be you're not linking all object modules together when you need to?
Also, remember that all virtual functions that are not declared pure need
to be defined. Did you define any of them or did you just declare them?

If none of that helps, we probably can't really help you, since (a) you
didn't post the whole code, and (b) your issue is compiler-specific,
apparently, so you might want to consider posting to 'gnu.g++.help'.

V

[David Harmon]

On Fri, 13 Jan 2006 14:34:38 +1300 in comp.lang.c++, mark
<tr*****@ihug.c o.nz> wrote,

I was under the impression if the virtual function is not defined in a
subclass, the parent class's function will be used.

Yes, however if you declare it in the subclass declaration, that
means you are promising to define it somewhere.

[mark]

In article <Hq************ ********@comcas t.com>,
"Victor Bazarov" <v.********@com Acast.net> wrote:

mark wrote:

I have this class:
class Selections {
OSStatus Init();

protected:
CFMutableSetRef selectionObject s;
static void CFASelectionsAp plier(const void* value, void* ctx);
OSType ready;
public:
Selections();
Selections(cons t Selections &obj);
virtual ~Selections();

virtual OSType GetSelectionSco pe();

virtual UInt32 GetSelectCount( SelectionFlag whichFlags);
virtual CFArrayRef GetSelObjects(S electionFlag whichFlags);
UInt32 GetCountOfClass (SelObjectClass theClass);
CFArrayRef GetSelObjectsOf Class(SelObject Class theClass);
virtual UInt32 GetCountOfScope (OSType theScope);
virtual CFArrayRef GetArrayofScope (OSType theScope);

virtual OSStatus MassAddSelObjec ts(CFArrayRef sorArray);
virtual OSStatus AddSelectededOb ject(SelectedOb jectRef soref);
virtual OSStatus MassRemoveSelOb jects(CFArrayRe f sorArray);
virtual OSStatus RemoveSelectedO bject(SelectedO bjectRef soref);
virtual void RemoveAllSelect edObjects(Selec tionFlag whichFlags);
void RemoveSelObject sOfClass(SelObj ectClass theClass);
virtual void RemoveSelObject sOfScope(OSType theScope);
virtual void RemoveAll();
};

and a subclass:

typedef class DirView DirView;

class DVSelections: public Selections {
DirView* view;
OSType dvsReady;
public:
DVSelections(Di rView* theView);
DVSelections(co nst DVSelections &obj);
~DVSelections() ;

OSType GetSelectionSco pe();
DirView* GetView();
};

When I attempt to compile it, the linker complains with this message:
/usr/bin/ld: Undefined symbols:
vtable for DVSelections

I was under the impression if the virtual function is not defined in a
subclass, the parent class's function will be used.
What am I missing?

Could it be you're not linking all object modules together when you need to?
Also, remember that all virtual functions that are not declared pure need
to be defined. Did you define any of them or did you just declare them?

If none of that helps, we probably can't really help you, since (a) you
didn't post the whole code, and (b) your issue is compiler-specific,
apparently, so you might want to consider posting to 'gnu.g++.help'.

V

All virtual functions for the base class have been declared and coded.

There is a function with this code:

OSStatus CreateNewDVSele ction(DirView* theView) {
if (theView==nil) {return paramErr;}
DVSelectionsRef dvs=nil;

try {
(1) dvs=new DVSelections(th eView);
}
catch (OSStatus OE) {
if (dvs) {delete dvs;}
return OE;
}
catch (...) {
if (dvs) {delete dvs;}
return memFullErr;
};

return 0;
};

Could (1) be causing the problem?

[Victor Bazarov]

mark wrote:

In article <Hq************ ********@comcas t.com>,
"Victor Bazarov" <v.********@com Acast.net> wrote:

mark wrote:

I have this class:
[..]
I was under the impression if the virtual function is not defined
Virtual functions have to be either declared *pure* or defined (or both).
You cannot have a virtual function not defined, and not pure.
in a subclass, the parent class's function will be used.
What am I missing?

That's what you're missing. You need to define all functions that are
not pure.
Could it be you're not linking all object modules together when you
need to? Also, remember that all virtual functions that are not
declared pure need to be defined. Did you define any of them or did
you just declare them?

If none of that helps, we probably can't really help you, since (a)
you didn't post the whole code, and (b) your issue is
compiler-specific, apparently, so you might want to consider posting
to 'gnu.g++.help'.

V
All virtual functions for the base class have been declared and coded.

What do you mean by "coded"? Defined? Are you linking the module where
they are defined into your program?

There is a function with this code:

OSStatus CreateNewDVSele ction(DirView* theView) {
if (theView==nil) {return paramErr;}
What is 'nil'?
DVSelectionsRef dvs=nil;
What is 'nil'? What is 'DVSelectionsRe f'?
try {
(1) dvs=new DVSelections(th eView);
}
catch (OSStatus OE) {
if (dvs) {delete dvs;}
return OE;
}
catch (...) {
if (dvs) {delete dvs;}
return memFullErr;
};

return 0;
};

Could (1) be causing the problem?

No. The code itself if fine. The fact that you didn't define all
the virtual functions, or didn't provide the definitions to the linker,
is the problem.

V

[mark]

In article <BM************ ********@comcas t.com>,
"Victor Bazarov" <v.********@com Acast.net> wrote:

mark wrote:

In article <Hq************ ********@comcas t.com>,
"Victor Bazarov" <v.********@com Acast.net> wrote:

mark wrote:
I have this class:
[..]
I was under the impression if the virtual function is not defined
Virtual functions have to be either declared *pure* or defined (or both).
You cannot have a virtual function not defined, and not pure.
in a subclass, the parent class's function will be used.
What am I missing?

That's what you're missing. You need to define all functions that are
not pure.

Thanks. Now I get it.

What is 'nil'?

Old pascal name for NULL.

[mark]

In article <44************ ****@news.west. earthlink.net>,
David Harmon <so****@netcom. com> wrote:

On Fri, 13 Jan 2006 14:34:38 +1300 in comp.lang.c++, mark
<tr*****@ihug.c o.nz> wrote,

I was under the impression if the virtual function is not defined in a
subclass, the parent class's function will be used.

Yes, however if you declare it in the subclass declaration, that
means you are promising to define it somewhere.

I didn't define the virtual in the subclass, only the base class (and
it's not pure).

[Greg]

mark wrote:

In article <44************ ****@news.west. earthlink.net>,
David Harmon <so****@netcom. com> wrote:

On Fri, 13 Jan 2006 14:34:38 +1300 in comp.lang.c++, mark
<tr*****@ihug.c o.nz> wrote,

I was under the impression if the virtual function is not defined in a
subclass, the parent class's function will be used.

Yes, however if you declare it in the subclass declaration, that
means you are promising to define it somewhere.

I didn't define the virtual in the subclass, only the base class (and
it's not pure).

If a function is declared virtual in a base class, it is also virtual
in every derived class whether or not the derived class uses the
"virtual" keyword in its declaration of the function.

I suspect that you have not defined the (virtual) destructor for
DVSelections anywhere.

Greg

[mark]

In article <11************ **********@g49g 2000cwa.googleg roups.com>,
"Greg" <gr****@pacbell .net> wrote:

mark wrote:

In article <44************ ****@news.west. earthlink.net>,
David Harmon <so****@netcom. com> wrote:

On Fri, 13 Jan 2006 14:34:38 +1300 in comp.lang.c++, mark
<tr*****@ihug.c o.nz> wrote,
>I was under the impression if the virtual function is not defined in a
>subclass, the parent class's function will be used.

Yes, however if you declare it in the subclass declaration, that
means you are promising to define it somewhere.

I didn't define the virtual in the subclass, only the base class (and
it's not pure).

If a function is declared virtual in a base class, it is also virtual
in every derived class whether or not the derived class uses the
"virtual" keyword in its declaration of the function.

I suspect that you have not defined the (virtual) destructor for
DVSelections anywhere.

DOH! DOH! DOH! DOH!
Looked over the code a dozen times and missed this little detailed
completely.
Thanks. Greg

[CodeSafe]

Bahhh
if you want to create a pure virtual interface with pure virtual
destructor do
..h file:

class IMyPureVirtualC lass
{
public:
virtual ~IMyPureVirtual Class() = 0;

virtual void SomeInterfaceFu nction() = 0;
//...
};

..cpp file:
IMyPureVirtualC lass::~IMyPureV irtualClass()
{
//empty destructor (declared as pure virtual)
}

now, when implementing the interface you should keep interface
functions virtual.
destructors in class declerations should ALWAYS be virtual or else they
might not get called, and it might cause mem leaks.

cheers
mark wrote:

In article <11************ **********@g49g 2000cwa.googleg roups.com>,
"Greg" <gr****@pacbell .net> wrote:

mark wrote:

In article <44************ ****@news.west. earthlink.net>,
David Harmon <so****@netcom. com> wrote:

> On Fri, 13 Jan 2006 14:34:38 +1300 in comp.lang.c++, mark
> <tr*****@ihug.c o.nz> wrote,
> >I was under the impression if the virtual function is not defined in a
> >subclass, the parent class's function will be used.
>
> Yes, however if you declare it in the subclass declaration, that
> means you are promising to define it somewhere.
>

I didn't define the virtual in the subclass, only the base class (and
it's not pure).

If a function is declared virtual in a base class, it is also virtual
in every derived class whether or not the derived class uses the
"virtual" keyword in its declaration of the function.

I suspect that you have not defined the (virtual) destructor for
DVSelections anywhere.

DOH! DOH! DOH! DOH!
Looked over the code a dozen times and missed this little detailed
completely.
Thanks.

Greg