Passing Arrays from VB to C++DLL

[Kurt Richardson]

Hi all

Sorry to bother you with what is probably a really
trivial question for you C++ experts. My programming
skill are pretty amateur, but I'm pretty good at VB.NET.
However, I'm wanting to realise some of the speed
benefits of writing some of my routines in C++ and
accessing them from my VB software.

I have managed to do this with a few simple routines in
which variables are passed... no arrays.

However, I am currently working on a routine that
requires that I pass an array to the C++ DLL and then
back again to the main VB program (I actually want to
pass several arrays, but I only want to manipulate one of
them). The C++ routine needs to dynamically resize the
array to sizes that can only be decided during runtime.
In VB this is simply done with ReDim Preserve, but my C++
Bible (Horton's Beginning Visual C++) seems to indicate
that I need to use pointers, duplication, etc. and even
if I get that to work how will VB know that the array has
been resized?

Any assistance is much appreciated - though please keep
your answers at the 'dummies guide' level :-)

Thanks, Kurt

[Adam Mitz [MSFT]]

If you're going to use Managed Extensions for C++ then any .NET objects can be passed between code written in either language quite easily.

You'll probably want to use System.Collections.ArrayList since it is resizeable (.NET arrays are not). See
ms-help://MS.VSCC.2003/MS.MSDNQTR.2003FEB.1033/cpguide/html/cpconarraylist.htm
in the Visual Studio help system.

To call functions in C++, create a C++ .NET Class Library project. This will result in a DLL. Add a reference to the DLL in your VB project.

I hope this is clear enough, please reply if you have further questions.

Adam Mitz
Microsoft
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Subject: Passing Arrays from VB to C++DLL
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Hi all

Sorry to bother you with what is probably a really
trivial question for you C++ experts. My programming
skill are pretty amateur, but I'm pretty good at VB.NET.
However, I'm wanting to realise some of the speed
benefits of writing some of my routines in C++ and
accessing them from my VB software.

I have managed to do this with a few simple routines in
which variables are passed... no arrays.

However, I am currently working on a routine that
requires that I pass an array to the C++ DLL and then
back again to the main VB program (I actually want to
pass several arrays, but I only want to manipulate one of
them). The C++ routine needs to dynamically resize the
array to sizes that can only be decided during runtime.
In VB this is simply done with ReDim Preserve, but my C++
Bible (Horton's Beginning Visual C++) seems to indicate
that I need to use pointers, duplication, etc. and even
if I get that to work how will VB know that the array has
been resized?

Any assistance is much appreciated - though please keep
your answers at the 'dummies guide' level :-)

Thanks, Kurt

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