interop, Problem passing string as BSTR string to C DLL - Nullreference exception

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interop >> Problem passing string as BSTR string to C DLL - Nullreference exception

by msnews.microsoft.com » Tue, 11 Apr 2006 15:33:06 GMT

Platform: VB.Net 1.1

I am trying to pass a string in VB.Net to a C Dll method which accepts a
BSTR. I get a nullreference exception whenever I call the API.

The following VBA declaration works fine in my previous Application:
Dim ddl As String
...
set_DatafilePath (ddl)

...
Declare Sub set_DatafilePath Lib "mydll.dll" (ByVal datafilepath As String)

In VB.Net, I have tried following:
String path = "somepath"
set_DatafilePath (path)

a) Declare Sub set_DatafilePath Lib "mydll.dll" ( ByVal datafilepath As
String)
b) Declare Sub set_DatafilePath Lib "mydll.dll" (
<MarshalAs(UnmanagedType.BStr)> ByVal datafilepath As String)
c) <DllImport("mydll.dll", CharSet:=CharSet.Auto)> _ 'Have tried ANSI as
well as Unicode as well
Public Shared Sub set_DatafilePath(<MarshalAs(UnmanagedType.BStr)> ByVal
datafilepath As String)
End Sub
d) <DllImport("mydll.dll", CharSet:=CharSet.Auto)> _
Public Shared Sub set_DatafilePath( ByVal datafilepath As String)
End Sub

Any help would be appreciated.

Cheers,

Manish Jain
XXXX@XXXXX.COM


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interop >> Problem passing string as BSTR string to C DLL - Nullreference exception

by Dmytro Lapshyn [MVP] » Tue, 11 Apr 2006 21:32:12 GMT


Hi!

Here's how Microsoft recommends such functions to be declared (taken from
MSDN):

Public Declare Auto Sub PassBStr Lib "StringLib.Dll" _
(<MarshalAs(UnmanagedType.BStr)> s As String)
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