Re: Passing a 2d array from vb.net to unmanaged C++ dll

From:
"Alexander Nickolov" <agnickolov@mvps.org>
Newsgroups:
microsoft.public.vc.language
Date:
Thu, 26 Apr 2007 12:03:12 -0700
Message-ID:
<uToZKWDiHHA.3960@TK2MSFTNGP02.phx.gbl>
If you are using the COM Interop, the answer is a safe array.
Safe arrays can be multi-dimensional and there's a standard API
(Automation) to access them from C++, and COM Interop
supports them (AFAIK, never used .NET myself) as well.

You may consider posting this question in the interop group
where it belongs:

microsoft.public.dotnet.framework.interop

--
=====================================
Alexander Nickolov
Microsoft MVP [VC], MCSD
email: agnickolov@mvps.org
MVP VC FAQ: http://vcfaq.mvps.org
=====================================

"Andrei" <andrei.toma@era-environmental.com> wrote in message
news:OwKAjIAiHHA.5048@TK2MSFTNGP03.phx.gbl...

Hi,

I'm trying to pass a bi-dimensional array of integers from vb.net to a c++
dll (in fact - a matrix that has to be processed in the dll) and then I
need the results back in the vb.net application.
I tried using the same approach as when passing a simple array (see
example below) but didn't succeed.

C++ function to process the array:
int Cmfcw001App::TestArr(int *ar, int size) {

//read the first element for test

int k;

k = ar[5];

return k;

}

.....

The function TestArr has been defined in the .def file.

The declaration in vb.net module

Public Declare Function TestArr Lib "<path>\mfcw001.dll" (ByRef ar As
Integer, ByVal size As Integer) As Integer

//****** Usage in vb.net code:

Dim ar(9) As Integer

For i = 0 To 9

ar(i) = -1 * i

Next

s = TestArr(ar(0), 10)

MsgBox(s)

On this pattern I tried replacing
int* ar with int** ar ,
ar(9) with ar(3, 3)
the call is now TestArr(ar(0, 0), 10)
in the dll the function tries to read k = ar[0][0]

The error message I get in vb.net is "Object reference not set to an
instance of an object" when reaching the call to TestArr.

Can anybody help, please ?

Thank you,

Andrei.

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