[Mono-list] Re: [Mono-dev] PInvoke : argument passing by ref

[Zoltan Varga]

                                        Hi,

 The way mono marshalls data from/to native code is described here:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnnetcomp/html/netcfmarshallingtypes.asp

If things don't work that way in mono, than it is a bug and we will fix it.

If you pass structures to native code using 'ref', then you can use
the [In, Out]
attributes to specify whenever changes made in native code are visible
to managed code,
ie.

void foo ([In] ref AStruct s).

This doesn't work in 1.1.9, but it works in the SVN version, see this bug:

http://bugzilla.ximian.com/show_bug.cgi?id=76502

           Zoltan

On 10/23/05, Shankari <shankari82 at yahoo.com> wrote:
> Hello,
>
> I am trying to isolate the updates by unmanaged code
> if the arguments are passed by reference in Pinvoke.
>
> I looked up marshal.c and at
> mono_marshal_emit_native_wrapper , the by-ref
> argumments are being marshalled back to managed
> memory.
>
> I am trying to do this by the foll :
>
> After the C code has made the updates : when the
> results are being marshalled back to the managed
> object, I can copy this to a diff location  and return
> this address and thus prevent the original argument
> from being updated.
>
>
> I could do this at call time , by copying the managed
> structure to another location and passing this
> addr...and this can get updated..but in this case I
> have to change the final byref argument to point to
> this new address.
>
>
> Everything leads to mono_mb_emit_byte( where some copy
> actually seems to be happening..) but it emits IL code
> and it *seems* to be pushing similar stuff if I pass
> by value or by reference.
>
>
>
> Any pointers on how to achieve my objective ??
>
>
> Thanks,
>
>
>
>
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