String format and unmanaged DLL

[Thomas]

Hi group!

I've a problem calling a function in a unmanaged DLL.

Here is the definition of the function I want to use, as it is written
in the documentation :
char Identify(char * ID)
ID : points to a buffer that receives the string. The buffer must have
sufficient space for the string and a terminating null character.

Here is my code in VB.NET to declare the function :
<DllImport("DllToUse.dll", CharSet:=CharSet.Unicode)> _
Private Shared Function IdentifyReader(ByVal Identity As
StringBuilder)As Integer
End Function

Here is my code in VB.NET to call the function :
Dim IDReader As New StringBuilder(255)
Dim res As Integer

res = Identify(IDReader)
IdentifierLecteur = IDReader.ToString()

My problem is that IDReader only contains "white squares" (ASCII
Code=63 ?). I have no error message but the encoding of the string
seems to be incorrect.

Thank you for your help !

Thomas

 

[Chris Tacke, eMVP]

One part of the problem is your use of char. Since CE is Unicode, all
strings are going to be wchars, so you're bound to get major
inconsistencies.

 

[Thomas VUILLET]

Thanks for your quick answer !

Does it mean that I can't use this DLL with .NET ?
Is there no way to convert the chars into correct strings, or a
different way to declare the function ?

Thomas

 

[Paul G. Tobey [eMVP]]

Are you sure that the DLL is expecting ASCII strings and not Unicode
strings?

Paul T.

 

[Alex Feinman [MVP]]

You can declare your function like this:
<DllImport("DllToUse.dll", CharSet:=CharSet.Unicode)> _
Private Shared Function IdentifyReader(ByVal Identity As Byte())As Integer
End Function

Make sure you have preallocated array of a suffcient size.

After you have called the function, extract you string from it by calling
Encoding.GetString():
Dim buffer as Byte(1024)
IdentifyReader(buffer)
Dim Identity as String = System.Text.Encoding.ASCII.GetString(buffer)