Arrays

[avni]

Hi,

I am writing code that uses a DLL. The function is that uses the DLL, does not take any values in. It ouptputs a really long string. I have the same code in Visual C++, where the value that is returned is of type char[33].

How can I do the same in Visual Basic? I tried to define an array as follows:

option explicit
private HostId() as string

then the function definition in a module

Declare Function GenerateId Lib "PLId.DLL" (ByRef HostId() As String) As Long

this is how I'm using the function:

dim rc as long

rc = GenerateId(HostId())

This gives me an exception. If I define the array with the size like private HostId(33) as string, then the function gives me invalid function arguments error.

What I am doing wrong??? Please help!!!
Thank you in advance.
Avni

[Kyle Burns]

A VB String handles the array of characters for you. What you are telling the compiler in your declare (kind of) is long int GenerateId(char &HostId[][]);

[avni]

Hi,
That's what I thought too, but I keep getting errors when I declared the ID as just string.
I tried again to declare the ID as string, in both the function declaration and the function call. Now, the ID returns empty string....

Thank you
avni

[Kyle Burns]

Did you try sending it a "padded" string?

[avni]

Hi Kyle,

No. I don't really know how to do that...
Can you please provide an example???
Thank you for your help...

Avni

[Kyle Burns]

Just doing a little brushing up on my API. VB stores string variables with the C datatype BSTR. This is more than just an array of characters. The first four bytes are information on the size of the string. Most C/C++ functions that take a string argument expect a LPSTR. The book I'm reading says that VB will always pass strings by reference no matter what the declaration. If you specify ByRef, it will pass a reference to a BSTR. If you specify ByVal, it will pass a reference to a LPSTR. You might want to check this out.

[avni]

Hi Kyle,

If I pass the string in the DLL as byref, i get exception error... If I pass as byval, then my program gives error, invalid function arguments...

Thanks for all your help.

Avni

[Kyle Burns]

Dim sRetVal as string
sRetVal = Space$(33)
'call the function

[avni]

Hi Kyle,

Thank you very very much.... The code is working with the addition of that code snippet you wrote...
Thank you... I really appreciate all your help.

avni