A Question that really bothers me...

[j1230xz]

Ok now the problem is this.

I have compiled some old code with Visual Studio 2008 (the code was
originally writen in Visual Studio 6) and i have this error:

Error 1 error C2681: 'void *' : invalid expression type for
dynamic_cast c:\Works\BaCCTester\Dev\Addins\Utils
\CommonDataManipulators\Sources\CommonDataFree.cpp 121
CommonDataManipulators

and the problematic line of code is this:
....
FunctionResponse* pFunctionResponse =
ACE_dynamic_cast(FunctionResponse*, data);
....

So it is logicaly that dynamic_cast does not work for void-pointers
since when I converted the pointer to void I have given up all type
information. But what makes me think twice about the corectness of the
previous sentence is that this code compiles perfectly under Visual
Studio 6. I would like to know more about this issue so any help,
references, links and so are highly appriciated.

Thank You,
Nikola Tanev

 

[j1230xz]

ONE MORE THINK TO ADD:
RTTI is turned ON

 

[James Kanze]

Ok now the problem is this.

I have compiled some old code with Visual Studio 2008 (the
code was originally writen in Visual Studio 6) and i have this
error:

Error 1 error C2681: 'void *' : invalid expression type for
dynamic_cast c:\Works\BaCCTester\Dev\Addins\Utils
\CommonDataManipulators\Sources\CommonDataFree.cpp 121
CommonDataManipulators

and the problematic line of code is this:
...
FunctionResponse* pFunctionResponse =
ACE_dynamic_cast(FunctionResponse*, data);
...

So it is logicaly that dynamic_cast does not work for
void-pointers since when I converted the pointer to void I
have given up all type information. But what makes me think
twice about the corectness of the previous sentence is that
this code compiles perfectly under Visual Studio 6. I would
like to know more about this issue so any help, references,
links and so are highly appriciated.

The real question is what ACE_dynamic_cast is. I suspect that
it's a macro, and probably expands differently depending on the
compiler, but I really don't know.

 

[j1230xz]

The real question is what ACE_dynamic_cast is. I suspect that
it's a macro, and probably expands differently depending on the
compiler, but I really don't know.

--
James Kanze (GABI Software) email:[email protected]
Conseils en informatique orientée objet/
Beratung in objektorientierter Datenverarbeitung
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34

Yes it is a macro
# define ACE_dynamic_cast(TYPE, EXPR) dynamic_cast<TYPE> (EXPR)
actualy it is a standard dynamic_cast and it is from the ACE libraries

 

[Puppet_Sock]

Yes it is a macro
#   define ACE_dynamic_cast(TYPE, EXPR) dynamic_cast<TYPE> (EXPR)
actualy it is a standard dynamic_cast and it is from the ACE libraries

<InigoMontoyaVoice>You keep using that word. I do not think
it means what you think it means.</voice>

In this news group, "standard" means part of the standard
C++ language, not part of a commercial library, no matter
how many people use it.

As to your original question:
- Did you read the help files for VS?

Compiler Error C2681

A casting operator tried to convert from an invalid type.
For example, if you use the dynamic_cast operator to
convert an expression to a pointer type, the source
expression must be a pointer.

- Did you consider asking your question in a news group
dealing with VS?

As to what older versions of VS would do: Older versions
were feydasque but fun. Lots of whacky things they did,
for many reasons, most of which are a bit off topic here.
Socks

 

[j1230xz]

äá á?

<InigoMontoyaVoice>You keep using that word. I do not think
it means what you think it means.</voice>

In this news group, "standard" means part of the standard
C++ language, not part of a commercial library, no matter
how many people use it.

As to your original question:
- Did you read the help files for VS?

Compiler Error C2681


- Did you consider asking your question in a news group
dealing with VS?

As to what older versions of VS would do: Older versions
were feydasque but fun. Lots of whacky things they did,
for many reasons, most of which are a bit off topic here.
Socks

 

[Bo Persson]

Yes it is a macro
# define ACE_dynamic_cast(TYPE, EXPR) dynamic_cast<TYPE> (EXPR)
actualy it is a standard dynamic_cast and it is from the ACE
libraries

And now, what is FunctionResponse and data. Could any of them be void?


Bo Persson

 

[peter koch]

Ok now the problem is this.
I have compiled some old code with Visual Studio 2008 (the
code was originally writen in Visual Studio 6) and i have this
error:
Error   1       error C2681: 'void *' : invalid expression type for
dynamic_cast    c:\Works\BaCCTester\Dev\Addins\Utils
\CommonDataManipulators\Sources\CommonDataFree.cpp      121
CommonDataManipulators
and the problematic line of code is this:
...
FunctionResponse* pFunctionResponse =
ACE_dynamic_cast(FunctionResponse*, data); [snip]
The real question is what ACE_dynamic_cast is.  I suspect that
it's a macro, and probably expands differently depending on the
compiler, but I really don't know.

Yes it is a macro
#   define ACE_dynamic_cast(TYPE, EXPR) dynamic_cast<TYPE> (EXPR)
actualy it is a standard dynamic_cast and it is from the ACE libraries

<InigoMontoyaVoice>You keep using that word. I do not think
it means what you think it means.</voice>

In this news group, "standard" means part of the standard
C++ language, not part of a commercial library, no matter
how many people use it.

But we found out that it really was a dynamic_cast (the errormessage
itself did show that if you read carefull), and in that case the
question definitely is standard, no matter if this is hidden inside
some hideous macro.

As to your original question:
- Did you read the help files for VS?

Compiler Error C2681


- Did you consider asking your question in a news group
  dealing with VS?

This question would only be appropriate in case the answer here
indicated that VS has a nonstandard behaviour.

[snip]

/Peter

 

[Andrey Tarasevich]

information. But what makes me think twice about the corectness of the
previous sentence is that this code compiles perfectly under Visual
Studio 6.

VC6 reports the same error when 'dynamic_cast' is applied to a 'void*'
expression.

This means that it is absolutely impossible to figure out why it
compiled in VC6 from the information you provided so far. It could be
that in VC6 the expression was not 'void*' somehow. Or it could be that
in VC6 the macro was actually mapped to 'static_cast'. Or something else.

 

[peter koch]

Ok now the problem is this.

I have compiled some old code with Visual Studio 2008 (the code was
originally writen in Visual Studio 6) and i have this error:

Error   1       error C2681: 'void *' : invalid expression type for
dynamic_cast    c:\Works\BaCCTester\Dev\Addins\Utils
\CommonDataManipulators\Sources\CommonDataFree.cpp      121
CommonDataManipulators

and the problematic line of code is this:
...
FunctionResponse* pFunctionResponse =
ACE_dynamic_cast(FunctionResponse*, data);
...

So it is logicaly that dynamic_cast does not work for void-pointers
since when I converted the pointer to void I have given up all type
information. But what makes me think twice about the corectness of the
previous sentence is that this code compiles perfectly under Visual
Studio 6. I would like to know more about this issue so any help,
references, links and so are highly appriciated.

If data is of type void* or FunctionResponse is of type void, the code
above should not work.
Visual Studio 6 probably got this wrong - it is a very old compiler.

/Peter

 

[Andrey Tarasevich]

If data is of type void* or FunctionResponse is of type void, the code
above should not work.

I don't see why it shouldn't work when 'FunctionResponse' is really
'void'. Conversion to 'void*' is a part of the standard 'dynamic_cast'
functionality.

> Visual Studio 6 probably got this wrong - it is a very old compiler.

A quick experiment shows that its actually gets this right, meaning that
the real root of the problem lies elsewhere.

 

[j1230xz]

Thank you all very much.

I just converted VC6 project that compiles ok into VC2008 and tried to
compile. The error was what i got. However due to the complexity of
the external library i have used (ACE), the macro might be redefined
somewhere else. However this was not some blocking problem that i had,
it just bothered me so it was just natural to ask . Anyway at the
end it all comes as I suspected, since as my memory serves me: void
pointers do not have runtime type information and if you deliberately
convert a pointer to void, you just given up its rtti.


I am sorry if i have caused inconvinience by asking the question here,
but i thought this would be a copiler issue, considering the compiler
change from VC6 to VC2008.

My Best Regards,
and thank you all again

 

[Michael DOUBEZ]

(e-mail address removed) a écrit :

Thank you all very much.

I just converted VC6 project that compiles ok into VC2008 and tried to
compile. The error was what i got. However due to the complexity of
the external library i have used (ACE), the macro might be redefined
somewhere else.

I had a look into ACE (5.6.2) and this macro defined only once
(ace/config-macros.h). I suspect it is a MSVC6 issue.

Michael