Marshaling structure members

[Sin]

Hello everybody,

I'm currently trying to understand how marshaling can use used for accessing
Win32 API functions as well as custom C/C++ code we design which exposes
functions the same way as the Win32 API.

I figured how to use strings... No problem there, there was a couple undred
examples on the net. I have yet to find how to do the same with an array of
integers for example... Here's my test code :

C strucure I'm trying to match :

typedef struct {
char name[200];
long id;
double a;
bool b;
char c;
short d[100];
} struct1;
Here's the VB structure in it's current (non working) state :

<StructLayout(L ayoutKind.Seque ntial, CharSet:=CharSe t.Ansi, Pack:=4)> _
Private Structure struct1

<VBFixedString( 200), MarshalAs(Unman agedType.ByValT Str, SizeConst:=200) >
_
Public name As String

Public id As Int32
Public a As Double
Public b As Boolean
Public c As Char

<VBFixedArray(1 00), MarshalAs(Unman agedType.I2, SizeConst:=100) > _
Public d() As Int16

End Structure
Two different problems occur using this definition. First, the
Marshall.SizeOf () call on an instance of the structure gives me this msg:

An unhandled exception of type 'System.Argumen tException' occurred in
WindowsApplicat ion2.exe

Additional information: Le type struct1 ne peut pas être marshalé comme une
structure non managée ; il n'est pas possible de calculer une taille ou un
offset.

Rough traduction from french :

The struct1 type cannot be marshalled as an unmanaged type ; it is
impossible to calculate a size or an offet.

I don't quite understand why I get this message, or what it means for that
matter.
The second problem is that if I modify the member "d" from my C DLL, I get
the following error :

An unhandled exception of type 'System.TypeLoa dException' occurred in
WindowsApplicat ion2.exe

Additional information: Impossible de marshaler le champ d du type struct1 :
ce type ne peut pas être marshalé comme un champ structuré.

Rough traduction from french :

Unable to marshall the d "field" of struct1 : this type cannot be marshaled
as a structured "field".

I've been looking over MSDN and the internet all morning and I still can't
figure how to make this work...

Any help would be appreciated!

Alex.

[Armin Zingler]

"Sin" <br****@hotmail .com> schrieb

<VBFixedArray(1 00), MarshalAs(Unman agedType.I2, SizeConst:=100) >
_ Public d() As Int16

Does

<VBFixedArray(1 00), MarshalAs(Unman agedType.BYVALA RRAY, SizeConst:=100) > _
Public d() As Int16
work?

Marshal.sizeof( gettype(struct1 )) returns 420 then. Seems to be correct.
I don't know, but isn't the C type "long" (field 'id') also "long" in
VB.NET?

--
Armin

http://www.plig.net/nnq/nquote.html
http://www.netmeister.org/news/learn2quote.html

[Armin Zingler]

"Sin" <br****@hotmail .com> schrieb

<VBFixedArray(1 00), MarshalAs(Unman agedType.I2, SizeConst:=100) >
_ Public d() As Int16

Does

<VBFixedArray(1 00), MarshalAs(Unman agedType.BYVALA RRAY, SizeConst:=100) > _
Public d() As Int16
work?

Marshal.sizeof( gettype(struct1 )) returns 420 then. Seems to be correct.
I don't know, but isn't the C type "long" (field 'id') also "long" in
VB.NET?

--
Armin

http://www.plig.net/nnq/nquote.html
http://www.netmeister.org/news/learn2quote.html

[Sin]

> Does

<VBFixedArray(1 00), MarshalAs(Unman agedType.BYVALA RRAY, SizeConst:=100) > _
Public d() As Int16

work?

Marshal.sizeof( gettype(struct1 )) returns 420 then. Seems to be correct.
Yes!

I did have to change my boolean declaration, either of these work :

C++ bool (C++ base type) = <MarshalAs(Unma nagedType.U1)> Public b As Boolean
C++ BOOL (ie : macro for int) = Public b As Boolean

I don't know, but isn't the C type "long" (field 'id') also "long" in
VB.NET?

Not sure where I picked that from but I'm fairly sure VB.NET's Long (as
opposed to any other language I know of) is 64 bits, rather than the 32 bits
an experienced programmer has come to expect. I guess they're laying the
grounds for the 64 bit version of Windows... It's odd nonetheless..

In other words, an unmanaged C/C++ long (a standard one that is) is either
an integer or an Int32 (which I find clearer). You never know when they're
going to change Integer to a 64 bit either, so better be safe than sorry!

Thanks alot for clearing it up!

Alex.