Best way to Marshal a string for a VB wrapper

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M K - 14 Dec 2004 17:05 GMT

I am trying to wrap this function:
int KPDCIteratorFind(KPDCIteratorRef inIteratorRef, const char *inName,
KPDCOpaqueRef *outfoundItemRef);

I have everything except inName working. inName should be 'A pointer to a
null-terminated, 8-bit ASCII character string. This pointer must not be NULL.'

I tried creating a wrapper using 'inName As StringBuilder'. But it doesn't
seem to work. Any ideas?

Here's the code that calls my wrapper.
Dim attrName As New System.Text.StringBuilder(255)
attrName.Append("saveEnable")
myStatus = myPro4.KIteratorFind(Me.myPropIter, attrName, Me.myPropRef)

And in 'doesn't work', the function reports it can't find that 'attrName',
but it should. So I'm wondering if the marshalling isn't going right.

Reply to this Message

Eric Carlson - 14 Dec 2004 18:09 GMT

Try this:

[MarshalAs(UnmanagedType.LPStr)] ref string inName

> I am trying to wrap this function:
> int KPDCIteratorFind(KPDCIteratorRef inIteratorRef, const char *inName,
[quoted text clipped - 13 lines]
> And in 'doesn't work', the function reports it can't find that 'attrName',
> but it should. So I'm wondering if the marshalling isn't going right.

Reply to this Message

M K - 14 Dec 2004 19:21 GMT

In VB that would look like this. Thank you. That would normally be fine. Now
I have to figure out why the function still doesn't like it.

> Try this:
>
[quoted text clipped - 17 lines]
> > And in 'doesn't work', the function reports it can't find that 'attrName',
> > but it should. So I'm wondering if the marshalling isn't going right.

Reply to this Message

Eric Carlson - 14 Dec 2004 19:37 GMT

Can you give a little more detail... i.e. from what you've said it sounds
like you have some VB code that you are trying to call from .Net ? Are you
importing this function into .Net with dllimport?

Or do i have this all wrong?? :)

Reply to this Message

M K - 14 Dec 2004 20:43 GMT

It's an unmanaged C++ DLL that I'm trying to use in my managed VB app. I have
documentation for the DLL, but it's all C++, not my first language.

What you gave me helped, with something else. The unmanaged function I
posted here about should take a string and find that property in an iterator.
I can walk the iterator and find the property, but this unmanaged function
doesn't find it. I think I will manually search the iterator. (I believe
that's what the unmanaged function is doing anyways.)

But I used MarshalAs UnmanagedType.AsAny for another function that needed to
take a boolean.

> Can you give a little more detail... i.e. from what you've said it sounds
> like you have some VB code that you are trying to call from .Net ? Are you
> importing this function into .Net with dllimport?
>
> Or do i have this all wrong?? :)

Reply to this Message

Eric Carlson - 14 Dec 2004 21:45 GMT

So, where are you at right now...

Does your function execute without error?
Does it just return and tell you that it couldn't find the item?
Are you absolutely sure that you are marshalling all of the parameters
correctly? (i.e. the inName ? )

A lot of times functions can execute without error, though the data is not
being marshalled correctly so you get bad results.

Can you post your complete vb.net "KPDCIteratorFind" function here?

Reply to this Message

M K - 14 Dec 2004 22:15 GMT

Yes, I believe that is it. I do not believe the inName parameter is
marshalling correctly.

I don't have the KPDCIteratorFind function, as it is in unmanaged DLL that I
do not have the source code too.

Here is what the documentation gives me for this function:
int KPDCIteratorFind(KPDCIteratorRef inIteratorRef, const char *inName,
KPDCOpaqueRef *outfoundItemRef);

The function executes without error, it simple returns an int value other
than 0. According to the documentation, 0 means the function fired okay. The
int I get (201) means that it could not find the item.

I know the item is there, because I can see it walking the iterator.

> So, where are you at right now...
>
[quoted text clipped - 7 lines]
>
> Can you post your complete vb.net "KPDCIteratorFind" function here?

Reply to this Message

Eric Carlson - 15 Dec 2004 16:25 GMT

Ok, thank for that info... now post your vb.net import for this function, and
tell me the different ways that you have tried to marshal your inName string,
then i can hopefully give you some suggestions.

Reply to this Message

M K - 15 Dec 2004 17:13 GMT

Declare Auto Function KIteratorFind Lib "DCSPro4SLR.dll" Alias
"KPDCIteratorFind" (ByVal inIteratorRef As IntPtr,
<MarshalAs(UnmanagedType.LPStr)> ByRef inName As String, ByRef
outFoundItemRef As IntPtr) As Integer

I've also tried:
Declare Auto Function KIteratorFind Lib "DCSPro4SLR.dll" Alias
"KPDCIteratorFind" (ByVal inIteratorRef As IntPtr, ByRef inName As
StringBuilder, ByRef outFoundItemRef As IntPtr) As Integer

Thanks

> Ok, thank for that info... now post your vb.net import for this function, and
> tell me the different ways that you have tried to marshal your inName string,
> then i can hopefully give you some suggestions.

Reply to this Message

Eric Carlson - 15 Dec 2004 20:13 GMT

Have you tried sending the inName as ByVal ?

"KPDCIteratorFind" (ByVal inIteratorRef As IntPtr,
<MarshalAs(UnmanagedType.LPStr)> ByVal inName As String, ByRef
outFoundItemRef As IntPtr) As Integer

Reply to this Message

M K - 15 Dec 2004 21:21 GMT

Sorry, you are correct. I thought I had, but I went through one more time.
And it worked. Thank you.

> Have you tried sending the inName as ByVal ?
>
> "KPDCIteratorFind" (ByVal inIteratorRef As IntPtr,
> <MarshalAs(UnmanagedType.LPStr)> ByVal inName As String, ByRef
> outFoundItemRef As IntPtr) As Integer

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Best way to Marshal a string for a VB wrapper

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