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microsoft.public.dotnet.framework.interop

String members of structure not allowed?

Ray

6/27/2007 3:53:00 PM

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
5 Answers

SvenC

6/27/2007 4:19:00 PM

0

Hi,

> 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

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.

> 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.

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

--
SvenC

Ray

6/27/2007 4:36:00 PM

0

On Jun 27, 11:18 am, "SvenC" <S...@community.nospam> wrote:
> Hi,
>
> > 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
>
> 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.
>
> > 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.
>
> Structs should not have worked in VB6 as automation types, too. How is
> mylib.test_type defined in VB6?
>
> --
> SvenC

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

Ben Voigt [C++ MVP]

6/28/2007 3:55:00 AM

0


"SvenC" <SvenC@community.nospam> wrote in message
news:CF59DE5D-0E9B-494D-A150-518EB5D490E1@microsoft.com...
> Hi,
>
>> 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
>
> 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.

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.

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

Ray

6/28/2007 3:12:00 PM

0

On Jun 27, 10:55 pm, "Ben Voigt [C++ MVP]" <r...@nospam.nospam> wrote:
> "SvenC" <S...@community.nospam> wrote in message
>
> news:CF59DE5D-0E9B-494D-A150-518EB5D490E1@microsoft.com...
>
>
>
>
>
> > Hi,
>
> >> 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
>
> > 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.
>
> 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.
>
>
>
>
>
> >> 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.
>
> > Structs should not have worked in VB6 as automation types, too. How is
> > mylib.test_type defined in VB6?
>
> > --
> > SvenC- Hide quoted text -
>
> - Show quoted text -- Hide quoted text -
>
> - Show quoted text -

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.Runtime.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

SteveR

7/9/2007 6:50:00 AM

0

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:

> On Jun 27, 10:55 pm, "Ben Voigt [C++ MVP]" <r...@nospam.nospam> wrote:
> > "SvenC" <S...@community.nospam> wrote in message
> >
> > news:CF59DE5D-0E9B-494D-A150-518EB5D490E1@microsoft.com...
> >
> >
> >
> >
> >
> > > Hi,
> >
> > >> 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
> >
> > > 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.
> >
> > 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.
> >
> >
> >
> >
> >
> > >> 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.
> >
> > > Structs should not have worked in VB6 as automation types, too. How is
> > > mylib.test_type defined in VB6?
> >
> > > --
> > > SvenC- Hide quoted text -
> >
> > - Show quoted text -- Hide quoted text -
> >
> > - Show quoted text -
>
> 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.Runtime.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
>
>