Pass BSTR from C++ to C#

I have C# project "X" ,I have exposed methods in it to the C++ project "Y".

X has method signature as follows -

public void WriteInformation(string sInfo){m_logger.ErrorInfo("{0}", sInfo);}

As I am exporting it to a C++ using .TLB file I checked declaration of this method in .tlh file which generates on #import of .tlb file.

virtual HRESULT __stdcall WriteInformation (    /*[in]*/ BSTR sMsg ) = 0;

I am calling this method in C++ project and passsing argument as follows -

oLog->WriteInformation(BSTR("Info write successful"));

Issue here is the string passed from C++ always becomes garbage or null , I debugged it and I can see value of sInfo is always garbage or null.

Please let me know what method should be followed to pass string from C++ to C#.

1 Reply

Know the answer? Post it — somebody with the same question will find it here.

Sam Hobbs15y ago
You should call the C# function using managed code. That is not a requirement but it would make it easier. Can you do that?

If you do it using unmanaged code, then you need to read the BSTR documentation; it clearly explains why the code you are using does not work and what to do about it. I suggest however using managed code instead.
0