COM object that returns a string

[JustinInAtlanta@gmail.com]

Hello. I have written a Class Library in C# that has two methods:

GetNumber returns 17
GetName returns foo

I am able to add a reference to the COM object from an ASP.NET page,
call both methods, and display the correct results in labels on the
Web page.

I also want to be able to instantiate the COM object in a C++ program
and call both methods. I can instantiate the COM object successfully.
When I call GetNumber from the C++ program, I get 17. But, when I call
GetName, I get garbage. I am guessing this has something to do with
the marshalling and how it is handling strings. I need to be able to
call the GetName method in the C# COM object from my C++ program to
get foo.

Does anyone have any ideas how to resolve this? Thanks in advance for
your help.

Justin

[Nicholas Paldino [.NET/C# MVP]]

Re: COM object that returns a string

Justin,

Well, it shouldn't be too hard. However, you really should show the COM
component implementation, as well as the C++ code that is making the call.

--
- Nicholas Paldino [.NET/C# MVP]
- mvp@spam.guard. caspershouse.co m

<JustinInAtlant a@gmail.comwrot e in message
news:360ad15e-ac5a-4158-83b5-c92ac289c44e@x6 9g2000hsx.googl egroups.com...

Hello. I have written a Class Library in C# that has two methods:
>
GetNumber returns 17
GetName returns foo
>
I am able to add a reference to the COM object from an ASP.NET page,
call both methods, and display the correct results in labels on the
Web page.
>
I also want to be able to instantiate the COM object in a C++ program
and call both methods. I can instantiate the COM object successfully.
When I call GetNumber from the C++ program, I get 17. But, when I call
GetName, I get garbage. I am guessing this has something to do with
the marshalling and how it is handling strings. I need to be able to
call the GetName method in the C# COM object from my C++ program to
get foo.
>
Does anyone have any ideas how to resolve this? Thanks in advance for
your help.
>
Justin

[Willy Denoyette [MVP]]

Re: COM object that returns a string

<JustinInAtlant a@gmail.comwrot e in message
news:360ad15e-ac5a-4158-83b5-c92ac289c44e@x6 9g2000hsx.googl egroups.com...

Hello. I have written a Class Library in C# that has two methods:
>
GetNumber returns 17
GetName returns foo
>
I am able to add a reference to the COM object from an ASP.NET page,
call both methods, and display the correct results in labels on the
Web page.
>
I also want to be able to instantiate the COM object in a C++ program
and call both methods. I can instantiate the COM object successfully.
When I call GetNumber from the C++ program, I get 17. But, when I call
GetName, I get garbage. I am guessing this has something to do with
the marshalling and how it is handling strings. I need to be able to
call the GetName method in the C# COM object from my C++ program to
get foo.
>
Does anyone have any ideas how to resolve this? Thanks in advance for
your help.
>
Justin

System.String is marshaled as BSTR (length prefixed Unicode strings), do you
treat them as such at the client?

Willy.