Question about Visual Basic 6 and memory buffers

[severino]

Hello,

I have a DLL written in C++: one of its functions returns a pointer to a
memory buffer in form of a long value (32 bits); when calling this function
from within Visual Basic, which is the best way to let Visual Basic access
this existing buffer?

I know that Visual Basic lets define a memory buffers like this:
Dim buffer() As Byte
how can I initialize this buffer using the long value returned by the DLL?

Thanks in advance and Kind Regards

Severino

[penagate]

It's a bit hard to try and access it as such so your best bet is to use RtlMoveMemory to move the buffer contents into your VB buffer. Either that or pass a pointer to your VB buffer in the first place.

Declare Sub RtlMoveMemory Lib "kernel32" ( _
    ByRef lpvDest As Any, _
    ByRef lpvSrc As Any, _
    ByVal cbLen As Long _
)

[Merri]

You might be interested about the trick used in this code: InStrCount. Basically the code makes a fake SAFEARRAYHEADER, assings this to an Integer array using CopyMemory (RtlMoveMemory) and then we could virtually read memory from anywhere.

Noticeable is that BufStrHeader(1) = 2 tells the array to be used is an integer array (two bytes per item). Change to 1 and it works with a byte array.


And then the warning: doing this is pretty dangerous, so save often and don't blame us if you destroy your computer