You're correct - it does have those member functions. It's been a while
since I've used DOMString, so I guess we both stand corrected...
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 ??
06/11/2001
09:53 AM
Please
respond to
xerces-c-dev
I stand corrected and I apologize if I mislead any younger C++ developers.
I guess I haven't written to many base classes that didn't have a 'virtual'
function in it. 'dynamic_cast' doesn't require a 'pure virtual' method or
even to have the derived class override the base class 'virtual' method,
however. I guess that down low, 'dynamic_cast' is looking at the virtual
tables.
I thank Dave at lotus for pointing this out. Even older engineers can still
learn.
Dave, one question though on the 'DOMString::print()',
'DOMString::println()'. The header file I downloaded for Xerces-C 1.4 for
the MS platform does have those two methods in it. Are we on the same page
on this one?
> -----Original Message-----
> From: [EMAIL PROTECTED] [SMTP:[EMAIL PROTECTED]]
> Sent: Friday, June 08, 2001 9:13 PM
> To: [EMAIL PROTECTED]
> Subject: RE: sample for down casting DOM_Node to DOM_Entity ??
>
>
> 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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> > > >
> > > >
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> >
> >
> >
> >
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