C - VB type conversion problem?

[Markmcdade]

Hi, could anyone please shed some light on what I'm doing wrong?
I'm trying to get a true value from a C function, but it always returns false.

In my C DLL, I have the function header as

BOOL Open(PSTR filename)




in my VB project, I first have the declaration as:

private Declare Function OpenDB Lib "DataBase.dll" Alias "Open" (byval txtFile as string) as Long




and then, as a procedure:


private Sub Form_Load()
Dim opened as Long
opened = OpenDB("theDB")

If opened = 1 then
lblRecordCounter = "DATABASE OPENED"
else
lblRecordCounter = "DATABASE CLOSED"
End If
End Sub




I don't get any errors, just a "DATABASE CLOSED" all the time rather than a "DATABASE OPENED".
Can anyone please tell me what I'm doing wrong?

Thanks for any help


Mark.

[Crazy D]

Have you checked what the return value is?
Debug.Print OpenDB("theDB")

Crazy D :-)
"One ring rules them all"

[Lothar Haensler]

better change your VB code to

if opened = 0 then
...database closed"
else
... database opened
end if



even better: make your C-DLL an ActiveX dll and raise an error that can be trapped by the VB program. That way, you'd be able to give the VB client some useful error information.

[Markmcdade]

it's always = 0

[Crazy D @ Work]

Can you modify the dll to see if the parameters gets there correct?

Crazy D @ Work :-)

[Markmcdade]

I discovered that if a string is passed, the function looks for that name, and opens the file.
To create a new file, a null pointer must be passed. Any ideas how to do this?
I tried


openDB(null)

openDB("")




but none seemed to work.

To pass an empty string try to do with "vbNull". I havent tried this for calls,
but in comparisons it works. Have a try !

;-)