Problem with Cast

[AriZOnA]

Hi!
I have the following scenario:

class QWidget
{}

class GeneratedClass : public QWidget
{}

class AbstractPanel
{
virtual void AbsMethod() = 0;
}

class MyClass : public GeneratedClass , AbstractPanel
{
void AbsMethod() {;} // impl
}
I have the QWidget pointer, how can I cast it so that I can
make a call to the AbsMethod implemented by MyClass ?
thanx a lot ...
bye


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[Rolf Magnus]

AriZOnA wrote:

Hi!
I have the following scenario:

class QWidget
{}

class GeneratedClass : public QWidget
{}

class AbstractPanel
{
virtual void AbsMethod() = 0;
}

class MyClass : public GeneratedClass , AbstractPanel
Was the private inheritance from AbstractPanel intentional?
{
void AbsMethod() {;} // impl
}
I have the QWidget pointer, how can I cast it so that I can
make a call to the AbsMethod implemented by MyClass ?

I assume QWidget is polymorphic (Well, I know Qt :-) ) and the
inheritance from AbstractPanel was supposed to be public.
Use dynamic_cast:

if (MyClass* p = dynamic_cast<MyClass*>(thewidgetpointer))
p->AbsMethod();
else
std::cerr << "your QWidget isn't an instance of MyClass\n";

[Daniel T.]

"AriZOnA" <wa*@libero.it> wrote:

Hi!
I have the following scenario:

class QWidget
{}

class GeneratedClass : public QWidget
{}

class AbstractPanel
{
virtual void AbsMethod() = 0;
}

class MyClass : public GeneratedClass , AbstractPanel
{
void AbsMethod() {;} // impl
}
I have the QWidget pointer, how can I cast it so that I can
make a call to the AbsMethod implemented by MyClass ?

How do you know that the object in the QWidget pointer you have
implements the AbsMethod?

[tom_usenet]

On Wed, 14 Apr 2004 11:25:14 +0000 (UTC), "AriZOnA" <wa*@libero.it>
wrote:

Hi!
I have the following scenario:

class QWidget
{}

class GeneratedClass : public QWidget
{}

class AbstractPanel
{
virtual void AbsMethod() = 0;
}

class MyClass : public GeneratedClass , AbstractPanel
{
void AbsMethod() {;} // impl
}
I have the QWidget pointer, how can I cast it so that I can
make a call to the AbsMethod implemented by MyClass ?

Assuming QWidget has at least 1 virtual function (and surely it has a
virtual destructor), you can do:

if (MyClass* p = dynamic_cast<MyClass*>(qptr))
{
p->AbsMethod();
}

(or dynamic_cast to AbstractPanel instead).

Tom
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[Old Wolf]

tom_usenet <to********@hotmail.com> wrote:

"AriZOnA" <wa*@libero.it> wrote:

class QWidget
{}

class GeneratedClass : public QWidget
{}

class AbstractPanel
{
virtual void AbsMethod() = 0;
}

class MyClass : public GeneratedClass , AbstractPanel
{
void AbsMethod() {;} // impl
}

I have the QWidget pointer, how can I cast it so that I can
make a call to the AbsMethod implemented by MyClass ?
Assuming QWidget has at least 1 virtual function (and surely it has a
virtual destructor), you can do:

if (MyClass* p = dynamic_cast<MyClass*>(qptr))
{
p->AbsMethod();
}

If you expect qptr to always be a MyClass *, you can go:

dynamic_cast<MyClass &>(*qptr).AbsMethod();

which will throw a std::bad_cast exception if qptr was not a
MyClass *.
(or dynamic_cast to AbstractPanel instead).

Is it safe to "sideways" dynamic cast? I've only ever used it
where the cast-to class was a direct descendent of the cast-from class.

[tom_usenet]

On 14 Apr 2004 21:39:24 -0700, ol*****@inspire.net.nz (Old Wolf)
wrote:

Is it safe to "sideways" dynamic cast? I've only ever used it
where the cast-to class was a direct descendent of the cast-from class.

Yes, dynamic_cast can be used to cross-cast.

Tom
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