W32 Interop Advice Needed

[John Slagle]

I have an old Win32 Dll that want to pass a string back to my app
via one of the parameters (not the return value).

I am seeing one way to do this is to dereference a StringBuilder
instance. Is this possible in VB.NET?

Another possible way might be
<MarshalAs (UnmanagedType. VBByRefStr)>

Does anyone have any experience with this?

The documentation for the DLL includes a VB6 decleration
containing keyword 'ByVal' for the string parameter, so I assume
its not passing a BSTR, but rather an address for a null terminated
series of ASCII characters.

I cannot locate an example within the DLL's documentation to
verify that a string has to be presized within VB6 prior to calling
the DLL.

Any insight appreciated.

-John Slagle
-Denver, CO

[Dominique Vandensteen]

Re: W32 Interop Advice Needed

can't you simply use byref?

Public Declare Sub TheFuncation Lib "thedll.dll " (ByRef theString as
String)


dominique


"John Slagle" <jrslagle.remov eme@mindspring. com> wrote in message
news:umBqztZ8DH A.2308@TK2MSFTN GP11.phx.gbl...[color=blue]
> I have an old Win32 Dll that want to pass a string back to my app
> via one of the parameters (not the return value).
>
> I am seeing one way to do this is to dereference a StringBuilder
> instance. Is this possible in VB.NET?
>
> Another possible way might be
> <MarshalAs (UnmanagedType. VBByRefStr)>
>
> Does anyone have any experience with this?
>
> The documentation for the DLL includes a VB6 decleration
> containing keyword 'ByVal' for the string parameter, so I assume
> its not passing a BSTR, but rather an address for a null terminated
> series of ASCII characters.
>
> I cannot locate an example within the DLL's documentation to
> verify that a string has to be presized within VB6 prior to calling
> the DLL.
>
> Any insight appreciated.
>
> -John Slagle
> -Denver, CO
>
>
>
>
>
>[/color]

[John Slagle]

Re: W32 Interop Advice Needed


"Dominique Vandensteen" <domi.vds_inser t@tralala_tenfo rce.com> wrote in
message news:ORmtOva8DH A.360@TK2MSFTNG P12.phx.gbl...
[color=blue]
> can't you simply use byref?[/color]

I was stuck in a VB6 mindset. I kept taking out the ByVal and VS.NET kept
putting it back in.

Doing this:

Declare Function error4describe Lib _
"C4FOX.DLL" Alias "error4describe VB" ( _
ByVal c4%, _
ByVal errCode As Int16, _
ByVal extraInfo%, _
ByRef desc1$, _
<MarshalAs(Unma nagedType.LPStr )> ByRef desc2 As String, _
<MarshalAs(Unma nagedType.VBByR efStr)> ByVal desc3 As String _
) As Int16

I Get This (from IL dump):

int16 error4describe(
int32 c4,
int16 errCode,
int32 extraInfo,
string& marshal( ansi bstr) desc1,
string& marshal( lpstr) desc2,
string marshal( byvalstr) desc3)
cil managed preservesig

Originally, I didn't think the BStr was what I wanted ('BYVAL' in the VB6
declaration). But the 'VB' suffix in the Alias hints otherwise.

It does appear as though I can do whatever I need. I just have to
find the right combination.

Thanks.
[color=blue]
>
> Public Declare Sub TheFuncation Lib "thedll.dll " (ByRef theString as
> String)
>
>
> dominique
>
>
> "John Slagle" <jrslagle.remov eme@mindspring. com> wrote in message
> news:umBqztZ8DH A.2308@TK2MSFTN GP11.phx.gbl...[color=green]
> > I have an old Win32 Dll that want to pass a string back to my app
> > via one of the parameters (not the return value).[/color][/color]

[Tom Shelton]

Re: W32 Interop Advice Needed

On 2004-02-12, John Slagle <jrslagle.remov eme@mindspring. com> wrote:[color=blue]
> I have an old Win32 Dll that want to pass a string back to my app
> via one of the parameters (not the return value).
>
> I am seeing one way to do this is to dereference a StringBuilder
> instance. Is this possible in VB.NET?
>
> Another possible way might be
><MarshalAs (UnmanagedType. VBByRefStr)>
>
> Does anyone have any experience with this?
>
> The documentation for the DLL includes a VB6 decleration
> containing keyword 'ByVal' for the string parameter, so I assume
> its not passing a BSTR, but rather an address for a null terminated
> series of ASCII characters.
>
> I cannot locate an example within the DLL's documentation to
> verify that a string has to be presized within VB6 prior to calling
> the DLL.
>
> Any insight appreciated.
>
> -John Slagle
> -Denver, CO[/color]

Pass a System.Text.Str ingBuilder ByVal...

Dim sb As New StringBuilder(Y ourLengthHere)
YourFunction(sb )
Return sb.ToString()

HTH
--
Tom Shelton [MVP]
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