Re: about casting

From:
"Tony Johansson" <johansson.andersson@telia.com>
Newsgroups:
microsoft.public.vc.mfc
Date:
Thu, 04 Dec 2008 19:14:45 GMT
Message-ID:
<F_VZk.4585$U5.34390@newsb.telia.net>
Hello!

The COM dll that we use is an very old product that was developed for many
years ago
so we just use it without trying to understand how COM works.
Now we must do a little change because we must pass a new object into the
method InitRules2.
My background is in standard C++ and C# so I
hope to get help without having to understand COM.

I just want to know if it's possible to do this in any way
Handle_DS* m_handle_DS = handle_ds;
see my question below.

Normally in standard C++ doing this would be perfect legal
Handle_DS* m_handle_DS = handle_ds;

//Tony

"Giovanni Dicanio" <giovanniDOTdicanio@REMOVEMEgmail.com> skrev i
meddelandet news:e0t$iCkVJHA.2928@TK2MSFTNGP03.phx.gbl...

"Tony Johansson" <t.johansson@logica.com> ha scritto nel messaggio
news:eNfS%23TjVJHA.4812@TK2MSFTNGP05.phx.gbl...

I have a COM dll where I have some problem with casting for one method.
Below you see a signature for method InitRules2 which is a method that is
located in the COM dll and is called from C# asp.net web application.
STDMETHODIMP CSyntaxObj::InitRules2(IHandle_DS* handle_ds, BSTR Provider,
BSTR DataSource, BSTR UserId, BSTR Password, BSTR ProductID, BSTR
Revision, BSTR ApplicationID, BSTR ApplicationRev, BSTR SubfileID,
VARIANT_BOOL *bRes)
{
...
   Handle_DS* m_handle_DS = handle_ds;
...
}

I create this object handle_ds from C# by calling C-tor in the COM dll.
This object is then passed from C# as the first parameter in method
InitRules2
as you can see.
Here its called handle_ds and is of type Handle_DS.


From the two preceding threads, it is clear to me that you are trying to
do COM programming just "by guessing", which is IMHO wrong, and cause of
frustration.

It seems to me that some fundamental concepts of COM, like the concept of
COM *interfaces*, are not clear to you.

Before trying to create some "automatic" code using ATL wizards of Visual
Studio, if you really need COM programming, I would suggest you to start
learning the basic concepts of COM, which is not trivial and requires some
practice with the compiler (besides studying on some proper book).

The ATL newsgroup microsoft.public.vc.atl is the proper place to ask
questions about COM code developed using ATL (which is the primary tool
for COM development in C++, IMHO).

I think that using C++/CLI to interface your C++ code with .NET (C#, etc.)
is much easier than using COM (especially if you have to learn COM first).
C++/CLI is considered not much as a .NET first-class language (like C# or
VB.NET), but it is considered as the best tool to build bridging layers
between native code written in C++ and managed .NET code.

Giovanni

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