Migrating VC++ 6.0 apps to .NET

[Steve]

We are considering the ways to migrate our VC++ 6.0 applications to .NET
platform.
It would be nice to rewrite them completely in C#, but due to the time
constraints
this option is out of question. We started from rewriting some dll in C# in
Visual
Studio .NET. Now we face chalenges of interoperation between old VC++ 6.0
apps and new .NET C# components. To solve this problem we considered the
following options:

1) Recompile old VC++ 6.0 app in Visual Studio .NET without /CLR and use COM
introperability to connect this app and new .NET C# components. It works more
or less OK as long as new .NET C# component expose interfaces. But it is
extremely difficult to access just methods of the class whish is not exposed
as interface in .NET C# component. TBLexp automatically creates interfaces
for such classes and this is complete mess. One methods somehow become
property, names are hardly recognizable etc.

So I tried another approach.

2) Recompile old VC++ 6.0 app in Visual Studio .NET with /CLR and use "It
just works" approach. In this case I have no troubles to access interfaces or
classes from new .NET C# component. However I very quickly discovered the
managed/unmanaged code interaction nightmare. The new .NET C# component
methods of course require managed parameters, and rest of the old VC++
application code of course expects unmanaged types.

We don't want to convert the old VC++ application code to Managed C++ in one
shoot, so the idea was to keep old application code intact (may be with minor
changies) and just recompile it in Visual Studio .NET to gain easy access to
new .NET C# components.

But because of this managed/unmanaged hell I can't even make simple function
call to new .NET C# components. For example see the following code segment:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
unsigned char cMessage __gc[] = new unsigned char __gc[256];
unsigned char cResult __gc[] = new unsigned char __gc[256];
unsigned char cBuf __gc[] = new unsigned char __gc[256];

....

// Call to new .NET C# component
m_pCommInt->SendCommand(cMessage, &cResult ) ;

....

strncpy((unsigned char*)&cBuf[0], ((unsigned char*)&cResult[0]) + 3,
(int)cResult[2]);
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The last line causes error C2440: 'type cast' : cannot convert from
'unsigned char __gc *' to 'unsigned char *' Cannot convert a managed
type to an unmanaged type

I understand that strncpy doesn't understand managed types, but it means
that in
this case we won't be able easily migrate our old app to .NET platform. Lots
of
changies will be required to old app to make it interoperate with new .NET
C# component.

Are there other ways to make old VC++ 6.0 app to interoperate with new .NET
C# component?

Can anyone suggest a better way for old VC++ 6.0 app to interoperate with
new .NET C# component?

Can anyone suggest recommend a good example of old VC++ 6.0 app
interoperating with new .NET C# component?

Can anyone clearly explain how to fix code segment above with strncpy
function causing C2440 error?

Can anyone provide good examples how to convert array array of managed types
to unmanaged e.g. unsigned char cManaged __gc[] to unsigned char
cUnmanaged[256]?

Most of the examples and methods in MSDN are about other way around
situation when new .NET app calls old legacy component (P/Invoke etc).

[Ronald Laeremans [MSFT]]

You need to pin the arrays and then passed the pinnen version. You do that
by pinning one of the elements (by convention the first one).

See the docs for the __pin keyword.

Ronald Laeremans
Visual C++ team

"Steve" <St***@discussions.microsoft.com> wrote in message
news:EE**********************************@microsof t.com...

We are considering the ways to migrate our VC++ 6.0 applications to .NET
platform.
It would be nice to rewrite them completely in C#, but due to the time
constraints
this option is out of question. We started from rewriting some dll in C#
in
Visual
Studio .NET. Now we face chalenges of interoperation between old VC++ 6.0
apps and new .NET C# components. To solve this problem we considered the
following options:

1) Recompile old VC++ 6.0 app in Visual Studio .NET without /CLR and use
COM
introperability to connect this app and new .NET C# components. It works
more
or less OK as long as new .NET C# component expose interfaces. But it is
extremely difficult to access just methods of the class whish is not
exposed
as interface in .NET C# component. TBLexp automatically creates interfaces
for such classes and this is complete mess. One methods somehow become
property, names are hardly recognizable etc.

So I tried another approach.

2) Recompile old VC++ 6.0 app in Visual Studio .NET with /CLR and use "It
just works" approach. In this case I have no troubles to access interfaces
or
classes from new .NET C# component. However I very quickly discovered the
managed/unmanaged code interaction nightmare. The new .NET C# component
methods of course require managed parameters, and rest of the old VC++
application code of course expects unmanaged types.

We don't want to convert the old VC++ application code to Managed C++ in
one
shoot, so the idea was to keep old application code intact (may be with
minor
changies) and just recompile it in Visual Studio .NET to gain easy access
to
new .NET C# components.

But because of this managed/unmanaged hell I can't even make simple
function
call to new .NET C# components. For example see the following code
segment:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
unsigned char cMessage __gc[] = new unsigned char __gc[256];
unsigned char cResult __gc[] = new unsigned char __gc[256];
unsigned char cBuf __gc[] = new unsigned char __gc[256];

...

// Call to new .NET C# component
m_pCommInt->SendCommand(cMessage, &cResult ) ;

...

strncpy((unsigned char*)&cBuf[0], ((unsigned char*)&cResult[0]) + 3,
(int)cResult[2]);
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The last line causes error C2440: 'type cast' : cannot convert from
'unsigned char __gc *' to 'unsigned char *' Cannot convert a managed
type to an unmanaged type

I understand that strncpy doesn't understand managed types, but it means
that in
this case we won't be able easily migrate our old app to .NET platform.
Lots
of
changies will be required to old app to make it interoperate with new .NET
C# component.

Are there other ways to make old VC++ 6.0 app to interoperate with new
.NET
C# component?

Can anyone suggest a better way for old VC++ 6.0 app to interoperate with
new .NET C# component?

Can anyone suggest recommend a good example of old VC++ 6.0 app
interoperating with new .NET C# component?

Can anyone clearly explain how to fix code segment above with strncpy
function causing C2440 error?

Can anyone provide good examples how to convert array array of managed
types
to unmanaged e.g. unsigned char cManaged __gc[] to unsigned char
cUnmanaged[256]?

Most of the examples and methods in MSDN are about other way around
situation when new .NET app calls old legacy component (P/Invoke etc).