Returning a string from VC++ dll to VB

ikoonman

I have seen a few "examples" on the web for returning a string from a dll written in VC++ to VB, in particular an article written by Nick Skapura (posted on various VB sites).

My problem is that this article (which has very good working example of passing parameters between VB and C++ in general) does not cover passing a newly created string back to VB, but uses a memory address already allocated to a parameter passed into the dll function at the initial call, to return the string to vb.

Does anybody know of a good tutorial that will explain how to do this? Also, some tutorials talk abt using BSTR to return a string-like structure for VB to work with, and other tutorials talk abt only passing passing back the pointer address. Which is better for safe and stable VB-C++ communication (taking into consideration coding efforts to make each scenario work)

TIA

daymobrew

Why do you want to return a newly created string? Why not follow the method in the article where it sends a pointer to the string location? Many Windows API functions use this form.

ikoonman

daymobrew wrote:

Why do you want to return a newly created string? Why not follow the method in the article where it sends a pointer to the string location? Many Windows API functions use this form.

That would be ideal, but I haven't really seen any examples/tutorials where it returns pointer-to-string for use in VB. Do you perhaps have any links?

TIA

daymobrew

ikoonman wrote:

That would be ideal, but I haven't really seen any examples/tutorials where it returns pointer-to-string for use in VB. Do you perhaps have any links?

TIA

ikoonman wrote:

but uses a memory address already allocated to a parameter passed into the dll function at the initial call, to return the string to vb.

pointer == memory address.
I meant use Nick Skapura's example you found. It's a solution that works. Why don't you want to use that form?

ikoonman

daymobrew wrote:

pointer == memory address.
I meant use Nick Skapura's example you found. It's a solution that works. Why don't you want to use that form?

I understand that yes, but then I read up on Google Groups and a lot of people were complaining that you could only use the length of the buffer as passed in by the VB app - so i assume that meant that if the var declared in VB was STRING * 100, you pretty much had a buffer of 100 bytes for the C dll to populate and return. I want more than that (to a max of say 1 meg)

Beano

I havent read the article you mention but a string in VB is either fixed length or variable length. If the article mentions variable length strings then you have no problem as their max size is approx 2 billion characters. If it uses fixed length strings then you're out of luck as they have a max of 64K characters.