Status: Solved
Priority: Medium
Security: Public
Views: 53
Last Modified: 2016-08-22

[Help] Cannot retrieve a bstr* via com interface into a system.string in vb.net

Hello Everyone,

I am getting the following issue:
Cannot retrieve a bstr* via com interface into a system.string in vb.net

I tryed to use StringBuilder but then I get a compilation error.
I also did:

Dim Str as String = nothing

myobj.getMessage(Str)
--> result: nothing

Is there an equivalent like in c# using [ref] - > myobj.getMessage(ref Str); where this works as expected.

All inputs are welcome.
Thank you very much in advance.
Best regards
MiQi

festijazz

Asked: 2016-07-27

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Visual Basic.NET

1 Solution

LVL 12

funwithdotnetCommented: 2016-07-27

Try:
Dim Str as String = "something"
If you pass Nothing as a reference, your method might have trouble with it.

LVL 1

festijazzAuthor Commented: 2016-07-27

Hello,
this solution does not work, I get something back as result. This does not modify the string.

please help.
thank you.
Best regards.
MiQi

LVL 36

it_saigeDeveloperCommented: 2016-07-28

But you are not getting the string itself, rather you are getting the pointer. You need to retrieve the string value from the memory location that the pointer references. For that, .NET has some ready made helper methods in the System.Runtime.InteropServices namespace. The one that is of benefit to you is Marshal.PtrToStringBSTR(IntPtr).

-saige-

LVL 1

festijazzAuthor Commented: 2016-07-28

Hello,
Thank you for your comment, I just found the issue. It was not possible as like vb6 it won't work the same way. It was related to the odl definition. The parameter was only set [in] but should be [in, out]. Now it works nicely.

Thank you for your inputs but it related to the unmanaged code.
Hopefully not a big change to cover it.
Best regards.
MiQi