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From: Scott Ballard on 12 Apr 2010 10:40
Greetings,

I'm having difficulty marshalling strings in a C# COM server
(VS2008, .NET Framework 2.0) back to a VC++ 6.0 client application.
The C++ application wants to consume a single byte per character
string, but the C# application is sending it back as a two byte per
character string. Fundamentally I know what the problem is (C#
strings are UNICODE) I just don't know where/how to inject the code to
fix it. Unfortunately I can't touch the C++ application; it must
remain unchanged. It was written against a COM interface that defines
the method like this in the IDL:

HRESULT Foo([in] BSTR incoming, [out] BSTR* outgoing);

In C# the interface is defined like this:

void Foo([In, MarshalAs(UnmanagedType.BStr) string incoming,
[MarshalAs(UnmanagedType.BStr] out string outgoing);

I've tried different MarshalAs types and an ICustomMarshaler for the
"outgoing" string to no avail (I can provide additional details if
needed). The odd thing is the C# COM server has no trouble reading
the "incoming" string from C++. I'm really hoping someone can give me
a pointer or two on how to do this. Thank you very much for your
help.

Regards,

Scott B.
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