I have some existing vb6 code that I am moving to a .net dll for easy
access from both vb6 apps as well as vb.net apps. There are some
custom api calls that use structures that have strings in them. I
didn't think this would be a problem but I find that if I put a string
in a structure it is no longer usable through com interop in a vb6
application. Is this correct or am I doing something wrong.

..net example code:
Public Structure test_type
Public junk As String
Public hello As Short
End Structure

vb6 example code:
private sub command1_click()
dim test as mylib.test_type

test.junk = "12345"
test.hello = 1776
end sub

I get "Variable uses an automation type not supported in visual basic"
error as soon as I click the button. I set a break point on test.junk
= "12345" and it never makes it there.

Any help or guidance on this would be greatly appriciated.

Raymond

Hi,

In .Net structs are value types and can only consist of value type.
Make it a class and you can put ref types like String in there.

Structs should not have worked in VB6 as automation types, too. How is
mylib.test_type defined in VB6?

--
SvenC

On Jun 27, 11:18 am, "SvenC" <S... (AT) community (DOT) nospam> wrote:
Thanks for the Reply.

The mylib is simply the dll name that the above .net code is located
in. The vb6 project has a reference to it in the references list.

I'll create a class and see if it works in place of the structure in
the api call.
Thanks,
Raymond

"SvenC" <SvenC (AT) community (DOT) nospam> wrote

Total nonsense. A reference is itself just a value, and you certainly can
have references inside structs. The trouble is that there are many many
ways to pass a string through p/invoke, and you have to tell it which. I
think there's a MarshalAsAttribute that should come with good examples.

On Jun 27, 10:55 pm, "Ben Voigt [C++ MVP]" <r... (AT) nospam (DOT) nospam> wrote:
I'm glad to hear that it should be possible. The VB6 to .net upgrade
wizard translated:
MakeCode As String * MakeCodeSize_int_gc
to:
<VBFixedString(MakeCodeSize_int_gc),
System.Runtime.InteropServices.MarshalAs(System.Ru ntime.InteropServices.UnmanagedType.ByValArray,
SizeConst:=MakeCodeSize_int_gc)> Public MakeCode() As Char

This is what generates the "Variable uses an automation type not
supported in visual basic" error. Because of your message here I tried
other options including the SafeArray instead of ByValArray and it
works. It isn't size limited like it is supposed to be though. It
should be restricted to MakecodeSize_int_gc. If you know the proper
MarshalAs type for a fixed length string I would appreciate knowing. I
will play with it in the mean time and see if I can figure it out.

Thanks for the response.
Raymond

I use the following attributes and it works OK when I call it from C++ and
another developer has managed to call it succesfully from VB so give this a
try.

[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 50)]
public string Comment;
--
Steve


"Ray" wrote: