Question

I am working on a project where I need to convert C++ code to C#.

I came across _bstr_t in the code I would like to know how the equivalent in C#.

Answer 1

The _bstr_t class is a wrapper for the BSTR type. This is a string in OLE Automation that is standardized across languages.

That said, the equivalent type in .NET is a System.String.

The key is when interacting with it (or defining your interfaces for COM interop in .NET code), you’ll want to use the MarshalAsAttribute with a value from the UnmanagedType enumeration of UnmanagedType.BStr, like so:

// This is on an interface that is in unmanaged code.
public void DoSomething([MarshalAs(UnmanagedType.BStr] string myString);

Note that if your class is actually exposing the _bstr_t in a COM interface, then you should change it to expose a BSTR; _bstr_t is a helper class that isn’t meant to be exposed across interface boundaries. The BSTR is for that and the methods on _bstr_t are for handling the allocation and use of BSTR instances.