Re: [Dev-C++] newbie dynamic_cast question

[Sebastien M. <seb...@te...>]

Hi!

Ok, I just check documentation, it seems you can't use a dynamic cast
in your case because File is not a base type for Element (of course,
since Element is a base class for File :)

So maybe you should use static_cast, or directly a standard C cast
(personnaly, I found all the cast operator useless, even if it's more
safe, it's too boring too use them :) and I never got a problem with
cast, bugs are generally elsewhere :)

I can give you a good documentation, but it's in french, so if you can
read french, here it is:
http://www.developpez.com/c/megacours/x4009.html#AEN4058

Happy coding,
Sebastien.

On Sun, Dec 08, 2002 at 07:51:09AM +0100, tc...@gm... wrote:
> Hi all,
>=20
> I have a dynamic_cast problem and I am not comming forward since then i=
n=20
> my project. Therefore I decided too find some help here in ths ML.
>=20
> OK,
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> I actually want to implement the iterator design Pattern in order to=20
> iterate through abstract Elements of abstract CollectionObjects.=20
> Therefore I have a class Element and CollectionObject.
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> Now I have written some concrete implementing classes Directory and Fil=
e=20
> that are supposed to be both Elements, with the supplement that=20
> Directory is also a CollectionObject.
>=20
> So I have sth. like
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> class Element{...}
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> class FileSystem : public Element { }
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> class File : public FileSystem {...}
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> class Directory : public CollectionObject, public FileSystem { ... }
>=20
> Now I decided to include some Filters, Iteated elements should be=20
> matched by Patterns (abstract class). I have created for this one a=20
> PatternExtension concrete class. It all looks lie this:
>=20
> class Pattern {
> ...
> public:
> 	virtual bool match( Element *p_Element ) =3D 0;
> }
>=20
>=20
> class PatternExtension : public Pattern
> {
> 	...
> 	virtual bool match( Element *p_Element )
> 	{
> 		//here starts the problem:
> 		//writing this instruction is causes an Error from the 	=20
> 		//compiler. Therefore I have been looking in my doc.
> 		//and I am convince to be doing it properly....
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> 	    File *l_File;
>=20
> 	    if( l_File =3D dynamic_cast<File *>( p_Element ) !=3D NULL )
> 		{
> 		...
> 		}
> 	/*
> 		Compiler error message:
>=20
> PatternExtension.cpp:19: cannot dynamic_cast `p_Element' (of type `clas=
s=20
> fs::Element *') to type `class fs::File *'
> make[1]: *** [PatternExtension.o] Fehler 1
> make[1]: Verlassen des Verzeichnisses Verzeichnis=20
> =BB/work/Projects/C++/Project1/fs=AB
> make: *** [all] Fehler 2
> 	*/
> 	}
> }
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> Why then?
>=20
> I hope I wasn't too long and that I made myself clear enough. I would b=
e=20
> pleased for any hint, tip to help me comming forward.
>=20
> Thanx
>=20
> --
> Eric Tchepannou
>=20
>=20
>=20
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>=20

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