Passing data from C to VB

[Galyl]

Im using a C dll to retrieve data via a comm port. It passes back a pointer to an array of bytes after it has retreived the data. How do I use that pointer to access the data in the memory location in VB. At the moment the data is passed back in a stream of bytes, which is not very efficient. Please advise.

 

[MikeCox]

I can think of 2 things u can try:

1.) Recieve the C pointer as a VB Variant. Once the Variant is assigned to the pointer you should be able to treat it like an array.

2.) Modify the C function to return void and recieve the array via a pointer in the argument list, then pass the VB array ByRef for the C function to populate it. If you do this then it will be a Declare Sub, not Function.

I haven't done this before, but I've seen API functions use the 2nd approach so I know it's possible.

Hope that helps.

~Mike
Any man willing to sacrifice liberty for security deserves neither liberty nor security.

-Ben Franklin

 

[Galyl]

Thanks, Ill try that

 

[Galyl]

I tried declaring a variant variable in VB, and using that to accept the pointer. The variant then contains the size of the memory buffer and not the data. I did it as follows:

Private Declare Function GetData Lib "vc2vb.dll" () As Byte
function for returning pointer to array

BYTE *GetData()
{
return g_UIB->data_buf;
}
C function that returns pointer to array

Private vDataBuf as Variant
variable to contain array

vDataBuf = GetData
assigning poiter to variant

Is this the correct way to do it?

Please advise

 

[jmarler]

You need to use a SAFEARRAY datatype. That is what VB uses internally and it is also recognized by C++.

Here is a link that may give you some more infromation -

http://support.microsoft.com/default.aspx?scid=kb;EN-US;q131086

Check that one out, or just do a search in MSDN for SAFEARRAY. - Jeff Marler B-)