Microsoft COM in c#

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  Sam Hobbs16y agoPosted Nov 5, 2010, 7:31 PM

  Accepted answer

  
  VT_BSTR is not a type; it is a code that indicates that a variant object has a bstr in it. A bstr is always created by Windows, but I think that all striings in C# are like bstrs.
   
  So you need to check the documentation for use of the variant type in C#; that is, how to tell C# that a parameter is a variant.
   
  If the C# truly is a COM object, then you don't need to be concerned about details; just add a reference to the COM object and let C# take care of details. Are you sure it is a COM object?
   
• AK

  Achal Kumar10y agoPosted Jan 18, 2016, 2:37 AM

  When a string is sent from C# to COM . RCW will automatically convert it into BSTR string.

  You will always accept a C# string in COM as bstr. It doesn't need explicit conversion. 

   

  Regards,

  Achal 
• ZZ

  Zbynek Zahradnik12y agoPosted Mar 24, 2014, 5:00 AM

  
  You may want save yourself a lot of trouble by using an OPC client toolkit instead, something like : http://www.opclabs.com/products/quickopc/languages-and-tools/csharp 
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  Sam Hobbs16y agoPosted Nov 12, 2010, 4:30 AM

  I am sorry but if you want more details you need to provide relevant details. What does the C++ function look like in terms of what are it's parameters? Also, what type of interface does it use? Is it a COM object with a type library or is it a DLL without a type library?
  
• MM

  manju M16y agoPosted Nov 12, 2010, 2:10 AM

  Hi
  Thanks for your reply.
  My requirement is i need to fetch value from database and to write the value in AIM OPC server.
  The OPC server supports variant type only. 
  I need to convert the value which is in string in database to variant.
  when i referred some dcoument for AIM OPC server, it s given that the equivalent of string is vt_bstr. so i need to convert this into that.
  Wat reference i need to add or how to do this?