Re: Right way of passing unmanaged structures between managed and native code?

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Date: Wed, 31 Mar 2004 17:12:28 -0800

Thanks a lot Ronald,

That's a relief! I knew that __value struct may not be binary compatible
with struct and judging by the context of the article it most probably
should have been the topic. Though other people could be misled as I was. Is
anywhere an explicit statement regarding the matter? That would be nice to
know it's not going to change in the future.
BTW why are you saying that opaqueness of the type is the guarantee of
binary compatibility?

thanks,
v

"Ronald Laeremans [MSFT]" <ronaldl@online.microsoft.com> wrote in message
news:%23TGAna3FEHA.2208@TK2MSFTNGP09.phx.gbl...
> This article is talking about taking (in C++.Net version 7.x terms about
the
> layout between:
>
> __gc struct Foo
> {
> SomeType SomeMember;
> ...
> };
>
> or
>
> __value struct Foo
> {
> SomeType SomeMember;
> };
>
> And
>
> struct Foo
> {
> SomeType SomeMember;
> }
>
> And NOT about the latter definition compiled either with or without the
> /CLR switch.
>
> If you use ildasm on the latter type you will see that it is eximitted in
a
> CLR sense as an opqaue (i.e. empty type) with explicit layout and explicit
> size with the compiler generated code directly managing the layout. Which
is
> indeed guaranteed to be the same in either case.
>
> Ronald
>
> "Vladimir Kouznetsov" <vladimir.kouznetsov@ngrain.com> wrote in message
> news:OhyZgA2FEHA.3640@tk2msftngp13.phx.gbl...
> > Thank you Ronald,
> >
> > I found the following phrase
> >
>
(http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dv_vstecha
> > rt/html/vbtchtroubleshootingnetinteroperability.asp "Troubleshooting
.NET
> > Interoperability"): "Because Visual Studio .NET optimizes the way data
is
> > stored, the unmanaged representation of the structure does not always
> match
> > the managed representation". From that I concluded that either alignment
> or
> > order of members or both can be different for managed and unmanaged
code.
> If
> > I'm misinterpreting that, that probably should be clarified. Otherwise
if
> > that is incorrect I'm happy to know that.
> >
> > thanks,
> > v
> >
> > "Ronald Laeremans [MSFT]" <ronaldl@online.microsoft.com> wrote in
message
> > news:eFothx1FEHA.3064@tk2msftngp13.phx.gbl...
> > > Hi Vladimir,
> > >
> > > Unmanaged types are guaranteed to have the same representation
> regardless
> > of
> > > whether they are compiled with or without the /clr switch. What
> > > documentation or experiment makes you believe otherwise?
> > >
> > > Ronald Laeremans
> > > Visual C++ team
> > >
> > > "Vladimir Kouznetsov" <vladimir.kouznetsov@ngrain.com> wrote in
message
> > > news:%23hbHnueFEHA.3032@TK2MSFTNGP09.phx.gbl...
> > > > Hi group,
> > > >
> > > > It seems there are no guarantees that the same unmanaged structures
> have
> > > the
> > > > same binary representation for managed and native code. How do I use
> > them
> > > in
> > > > mixed-code assemblies? Is there just some compiler magic behind
> curtains
> > > > (IJW, some implicit marshalling, which can lead to a performance
> > > > degradation) or the data are binary compatible in these scenarios or
I
> > > > perhaps should use attributes to explicitly specify the layout
(which
> > BTW
> > > > may depend on compiler switches increasing complexity of
maintenance)?
> > > >
> > > > thanks,
> > > > v
> > > >
> > > >
> > >
> > >
> >
> >
>
>

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