Re: Returning structures by value in .NET with P/Invoke

> David Piepgrass wrote:
> > Maybe I'm the only one dealing with this issue, but I'll post it
anyway
> > for the record.
> >
> > I'd just like to add a new wrinkle to this old thread. It seems that
if
> > the structure you return has a constructor, then the C++ compiler
> > decides to add 4 to the number at the end of the exported name, and
thus
> > the C++ and C# exported names match. See, in the example below I
suggest
> > declaring an alias in your .def file:
> >
> >    _CSharp_CreateSquareBox@16 = _CSharp_CreateSquareBox@12
> >
> > BUT if the Box structure is given a constructor, the C++ compiler
will
> > (or at least might) decide to use the name
_CSharp_CreateSquareBox@16 in
> > the first place. Consequently the line in the .def file is not only
> > unnecessary but illegal and you get this linker output:
> >
> > warning LNK4197: export '_CSharp_CreateSquareBox@16' specified
multiple
> > times; using first specification
> > error LNK2001: unresolved external symbol _CSharp_CreateSquareBox@12
> >
> > Gee whiz, Microsoft does weird things. Also, when you give your
> > structure a constructor, the C++ compiler will give you a warning
> >
> This all strikes me as a bug in the CLR. Maybe you discuss this on a
> Microsoft .NET mailing list for confirmation and let us know the
> outcome? It is nearly impossible to auto generate code for this kind
of
> weirdness and it would be nice to get support for pass by value into
> swig. There isn't this kind of weirdness on Linux btw, I'm sure I got
> this working a few years ago with mono and Linux, but never took it
any
> further as it doesn't work on the MS platform.

I'm not suggesting that SWIG attempt to generate code for this; I just
wanted to complete the picture on this issue. If I may correct a
misconception in your comment: while there may be a bug in the CLR, the
issue I talk about here is entirely on the C++ side (how would the CLR
know if my C++ class has a constructor or not?). And IIRC, there is no
problem with passing structs by value--only with returning them.

I just put a bug report on Microsoft Connect:

https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?Fe
edbackID=345096

But in my experience, Microsoft fixes things rather slowly.


-------------------------------------------------------------------------
This SF.net email is sponsored by: Microsoft
Defy all challenges. Microsoft(R) Visual Studio 2008.
http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/
_______________________________________________
Swig-user mailing list
Swig-user@...
https://lists.sourceforge.net/lists/listinfo/swig-user