Sorry, but polymorphism has _everything_ to do with dynamic casting. If a
class has no virtual functions, it's not polymorphic, and you cannot use
dynamic_cast to do run-time type introspection.
If you don't believe me, why don't you try to put some of that code you've
been posting through your compiler and see what its says? For example,
Microsoft Visual C++ gives the following error:
void
foo(DOM_Node node)
{
DOM_Entity entity = dynamic_cast<const DOM_Entity&>(node);
}
--------------------Configuration: TestXSLT - Win32
Debug--------------------
Compiling...
process.cpp
V:\xml-xalan\c\src\TestXSLT\process.cpp(790) : error C2683: dynamic_cast :
'DOM_Node' is not a polymorphic type
..\..\..\..\..\..\xml-xerces\c\src\dom/DOM_Node.hpp(95) : see
declaration of 'DOM_Node'
Error executing cl.exe.
process.obj - 1 error(s), 0 warning(s)
If you're going to post advice/code samples on the list, you ought to at
least try it out before you post.
Dave
"Adams,
David" To: "'[EMAIL PROTECTED]'"
<dadae@allsta <[EMAIL PROTECTED]>
te.com> cc: (bcc: David N Bertoni/CAM/Lotus)
Subject: RE: sample for down casting
DOM_Node to DOM_Entity ??
06/08/2001
05:40 PM
Please
respond to
xerces-c-dev
class CDOM_EXPORT DOM_Entity: public DOM_Node {
.
.
.
.
};
polymorphism has nothing to do with dynamically casting up and down a class
heirarchy tree. You might want to downcast to access methods in the derived
type, they don't have to be polymorphic methods.
> -----Original Message-----
> From: [EMAIL PROTECTED] [SMTP:[EMAIL PROTECTED]]
> Sent: Friday, June 08, 2001 4:07 PM
> To: [EMAIL PROTECTED]
> Subject: RE: sample for down casting DOM_Node to DOM_Entity ??
>
>
> You cannot use dynamic_cast with DOM_Node because it is not a polymorphic
> type. If your compiler lets you do this, you should throw it out and get
> a
> new one. The whole reason for using dynamic_cast is that you want
> run-time
> type casting, not compile-time type casting, so if this doesn't compile,
> it's probably not because the compiler figured out the actual type.
>
> There are lots of examples of "downcasts" in the sample code. If you
like
> old-style casts (which the Xerces code uses for portability), then use
> those:
>
> void
> foo(DOM_Node node)
> {
> if (node.getNodeType() == DOM_Node::ENTITY_NODE)
> {
> DOM_Entity ent = (DOM_Entity&)node;
> }
> }
>
> If you prefer new-style casts, which are safer, use those:
>
> void
> foo(DOM_Node node)
> {
> if (node.getNodeType() == DOM_Node::ENTITY_NODE)
> {
> DOM_Entity ent = static_cast<const DOM_Entity&>(node);
> }
> }
>
> Dave
>
>
>
>
>
> "Adams,
>
> David" To:
> "'[EMAIL PROTECTED]'" <[EMAIL PROTECTED]>
> <dadae@allsta cc: (bcc: David N
> Bertoni/CAM/Lotus)
> te.com> Subject: RE: sample for down
> casting DOM_Node to DOM_Entity ??
>
>
> 06/08/2001
>
> 04:42 PM
>
> Please
>
> respond to
>
> xerces-c-dev
>
>
>
>
>
>
>
>
> No it is not safe. That is the old style of casting. With that style I
> could
> do something like this:
> int x = 1;
> DOM_Node n = (DOM_Node)x; // which you know is not right.
>
> I suggest you use the following:
> DOM_Entity domen = dynamic_cast<DOM_Entity>(node);
> If it doesn't compile, it may be that the compiler is trying to tell you
> that 'node' may NOT be a DOM_Entity type and you are doing an illegal
> cast.
>
> Regarding the blank screen, in your example, if 'node' is not a
DOM_Entity
> type, you could be corrupting your screen memory.
>
> > -----Original Message-----
> > From: Awasthi, Anand [SMTP:[EMAIL PROTECTED]]
> > Sent: Friday, June 08, 2001 3:33 PM
> > To: '[EMAIL PROTECTED]'
> > Subject: RE: sample for down casting DOM_Node to DOM_Entity
??
> >
> > thanks guys...
> >
> > i tried
> >
> > DOM_Node node;
> > DOM_Entity domen = (DOM_Entity &)(node);
> >
> > its compiles...but is this safe ??
> >
> > later on i want to print PublicId and SystemId associated with this
> Entity
> > node and
> > i coded following:
> >
> > cout << "public id " << ((DOM_Entity &)node).getPublicId().transcode()
> <<
> > endl;
> > cout << "system id " << ((DOM_Entity &)node).getSystemId().transcode()
> <<
> > endl;
> >
> > but I am getting blank screen . is the above code correct or is there
> any
> > better
> > implementation for obtaining PublicId and System Id value ?? pls
suggest
> > that.
> >
> > as a matter of fact when I use above DOMStrng.transcode() method to
> obtain
> >
> > NOde Name ...i get Node Name. But when I try to obtain Node Value thru
> > getNodeValue().transcode(),
> > I get blank screen..whats wrong ??
> >
> >
> >
> > pls enlighten me
> >
> >
> > thanks
> > anand
> >
> >
> >
> >
> >
> >
> > -----Original Message-----
> > From: Adams, David [mailto:[EMAIL PROTECTED]]
> > Sent: Friday, June 08, 2001 3:24 PM
> > To: '[EMAIL PROTECTED]'
> > Subject: RE: sample for down casting DOM_Node to DOM_Entity ??
> >
> >
> > Curt is correct, in that I am assuming you know that the Node is an
> > DOM_Entity type node and was passed around your code as a DOM_Node and
> you
> > simply want to get its derived type back. If you do not know what type
> it
> > really is, you do have to check it. The VC++ macro "DYNAMIC_DOWNCAST"
is
> > another way to check if that works for you.
> >
> > > -----Original Message-----
> > > From: Adams, David [SMTP:[EMAIL PROTECTED]]
> > > Sent: Friday, June 08, 2001 3:16 PM
> > > To: '[EMAIL PROTECTED]'
> > > Subject: RE: sample for down casting DOM_Node to DOM_Entity
??
> > >
> > > DOM_Node n = // some node;
> > > DOM_Entity e = dynamic_cast<DOM_Entity>(n);
> > >
> > > I do not know what compiler you are using, but you will need to set
> the
> > > /GR
> > > switch on VC++ compilers. This is done by going to Project->settings,
> > > select
> > > the C/C++ tab, select the C++ Language category, and click on "Enable
> > > Run-Time Type Information (RTTI)" to enable it.
> > >
> > > > -----Original Message-----
> > > > From: Awasthi, Anand [SMTP:[EMAIL PROTECTED]]
> > > > Sent: Friday, June 08, 2001 2:58 PM
> > > > To: '[EMAIL PROTECTED]'
> > > > Subject: sample for down casting DOM_Node to DOM_Entity ??
> > > >
> > > > Hi,
> > > >
> > > > could someone pls provide sample code for down casting DOM_Node to
> > > > DOM_Entity ??
> > > >
> > > > thanks
> > > > Anand
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
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