Calling mamaged C# code from Visual C

[Tim Nelson]

Hi,
I've got a legacy application written in C. I'd like to evolve the product
(as opposed to completely rewriting it) by adding new features using C#. Is
this possible? I know I should be able to call a managed-code DLL from C,
but I am unsure of the best way to do it, and also how I might marshal the
data between the two parts between the managed and unmanaged parts of the
application.
Can anyone point me in a direction?
Thanks.

[Christopher Kimbell]

We had a similar problem. We wanted ActiveX code written in Visual Studio 6
to communicate with a WebService in .NET.

The way we solved it was to create a Managed C++ dll that was also a regular
dll. Use the wizards to create a regular dll, then enable the support for
managed extensions.

The VS6 code calls functions in this dll which in turn calls the WebService.
The limitation of using a regular dll is that you can only use C types, no
CStrings. Since your code is written in C, this should not be a problem.

When implementing this we had a problem freeing memory allocated within the
DLL. From what I could understand, the runtime tracks which CRT the memory
was allocated on. In our case I think the managed DLL used VS.NET version
and the ActiveX used VS6.
In order to overcome this, we created a method called FreeMemory() in the
DLL, this frees the memory in the context of the DLL.
Chris
"Tim Nelson" <ti***************@softhome.net> wrote in message
news:eU**************@TK2MSFTNGP12.phx.gbl...

Hi,
I've got a legacy application written in C. I'd like to evolve the product (as opposed to completely rewriting it) by adding new features using C#. Is this possible? I know I should be able to call a managed-code DLL from C,
but I am unsure of the best way to do it, and also how I might marshal the
data between the two parts between the managed and unmanaged parts of the
application.
Can anyone point me in a direction?
Thanks.

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

Tim,

You have a few options here. If your code doesn't do anything too
tricky, you might be able to just add the /clr switch to the compiler
process and then you will automatically be able to access managed code.

Hope this helps.
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard.caspershouse.com

"Tim Nelson" <ti***************@softhome.net> wrote in message
news:eU**************@TK2MSFTNGP12.phx.gbl...

Hi,
I've got a legacy application written in C. I'd like to evolve the product (as opposed to completely rewriting it) by adding new features using C#. Is this possible? I know I should be able to call a managed-code DLL from C,
but I am unsure of the best way to do it, and also how I might marshal the
data between the two parts between the managed and unmanaged parts of the
application.
Can anyone point me in a direction?
Thanks.

[Tim Nelson]

Chris,
If I read between the lines here... I think you are saying I can't call a C#
managed DLL directly from C, I have to use a managed regular C++ DLL as a
wrapper, right?
"Christopher Kimbell" <a@b.c> wrote in message
news:40********@news.broadpark.no...

We had a similar problem. We wanted ActiveX code written in Visual Studio 6 to communicate with a WebService in .NET.

The way we solved it was to create a Managed C++ dll that was also a regular dll. Use the wizards to create a regular dll, then enable the support for
managed extensions.

The VS6 code calls functions in this dll which in turn calls the WebService. The limitation of using a regular dll is that you can only use C types, no
CStrings. Since your code is written in C, this should not be a problem.

When implementing this we had a problem freeing memory allocated within the DLL. From what I could understand, the runtime tracks which CRT the memory
was allocated on. In our case I think the managed DLL used VS.NET version
and the ActiveX used VS6.
In order to overcome this, we created a method called FreeMemory() in the
DLL, this frees the memory in the context of the DLL.
Chris
"Tim Nelson" <ti***************@softhome.net> wrote in message
news:eU**************@TK2MSFTNGP12.phx.gbl...

Hi,
I've got a legacy application written in C. I'd like to evolve the

product

(as opposed to completely rewriting it) by adding new features using C#.

Is

this possible? I know I should be able to call a managed-code DLL from C, but I am unsure of the best way to do it, and also how I might marshal the data between the two parts between the managed and unmanaged parts of the application.
Can anyone point me in a direction?
Thanks.

[Niki Estner]

C# dll's don't export functions the way C dll's do: they export classes
(which are not available to C).
So you can:
- Compile your C code in Managed C++ (the MC++ compiler understands about
anything the "old" C++ compiler did - I think they only switch the backend)
- Use a Managed C++ wrapper
- implement a COM interface in your C# class, and call that from C

Niki

"Tim Nelson" <ti***************@softhome.net> wrote in
news:OY**************@TK2MSFTNGP10.phx.gbl...

Chris,
If I read between the lines here... I think you are saying I can't call a C# managed DLL directly from C, I have to use a managed regular C++ DLL as a
wrapper, right?
"Christopher Kimbell" <a@b.c> wrote in message
news:40********@news.broadpark.no...

We had a similar problem. We wanted ActiveX code written in Visual Studio

6

to communicate with a WebService in .NET.

The way we solved it was to create a Managed C++ dll that was also a regular

dll. Use the wizards to create a regular dll, then enable the support for managed extensions.

The VS6 code calls functions in this dll which in turn calls the

WebService.

The limitation of using a regular dll is that you can only use C types, no CStrings. Since your code is written in C, this should not be a problem.

When implementing this we had a problem freeing memory allocated within

the

DLL. From what I could understand, the runtime tracks which CRT the memory was allocated on. In our case I think the managed DLL used VS.NET version and the ActiveX used VS6.
In order to overcome this, we created a method called FreeMemory() in the DLL, this frees the memory in the context of the DLL.
Chris
"Tim Nelson" <ti***************@softhome.net> wrote in message
news:eU**************@TK2MSFTNGP12.phx.gbl...

Hi,
I've got a legacy application written in C. I'd like to evolve the

product

(as opposed to completely rewriting it) by adding new features using

C#. Is

this possible? I know I should be able to call a managed-code DLL

from C, but I am unsure of the best way to do it, and also how I might marshal the data between the two parts between the managed and unmanaged parts of the application.
Can anyone point me in a direction?
Thanks.

[Tim Nelson]

Niki,
If I read between your lines.... I think you would recommened
in order of preference:

1. Compile with /clr
2. Managed C++ Wrapper
3. COM Interface

In that order, right ???

Thanks.

"Niki Estner" <ni*********@cube.net> wrote in message
news:eC*************@tk2msftngp13.phx.gbl...

C# dll's don't export functions the way C dll's do: they export classes
(which are not available to C).
So you can:
- Compile your C code in Managed C++ (the MC++ compiler understands about
anything the "old" C++ compiler did - I think they only switch the backend) - Use a Managed C++ wrapper
- implement a COM interface in your C# class, and call that from C

Niki

"Tim Nelson" <ti***************@softhome.net> wrote in
news:OY**************@TK2MSFTNGP10.phx.gbl...

Chris,
If I read between the lines here... I think you are saying I can't call a

C#

managed DLL directly from C, I have to use a managed regular C++ DLL as a wrapper, right?
"Christopher Kimbell" <a@b.c> wrote in message
news:40********@news.broadpark.no...

We had a similar problem. We wanted ActiveX code written in Visual Studio

6

to communicate with a WebService in .NET.

The way we solved it was to create a Managed C++ dll that was also a regular

dll. Use the wizards to create a regular dll, then enable the support

for managed extensions.

The VS6 code calls functions in this dll which in turn calls the

WebService.

The limitation of using a regular dll is that you can only use C types, no

CStrings. Since your code is written in C, this should not be a

problem.
When implementing this we had a problem freeing memory allocated

within the

DLL. From what I could understand, the runtime tracks which CRT the memory was allocated on. In our case I think the managed DLL used VS.NET version and the ActiveX used VS6.
In order to overcome this, we created a method called FreeMemory() in the DLL, this frees the memory in the context of the DLL.
Chris
"Tim Nelson" <ti***************@softhome.net> wrote in message
news:eU**************@TK2MSFTNGP12.phx.gbl...
> Hi,
> I've got a legacy application written in C. I'd like to evolve the
product
> (as opposed to completely rewriting it) by adding new features using C#. Is
> this possible? I know I should be able to call a managed-code DLL

from

C,

> but I am unsure of the best way to do it, and also how I might

marshal the

> data between the two parts between the managed and unmanaged parts

of the

> application.
> Can anyone point me in a direction?
> Thanks.
>
>