does PInvoke support for polymorphism ?

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yaron - 11 Jun 2005 13:46 GMT

Hi,

I want to use my unmanaged c++ class library from a c# client.
my unmanaged c++ class library use polymorpism, is this polymorphism also
exported to my c# client via PInvoke ?

thanks.

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Carl Daniel [VC++ MVP] - 11 Jun 2005 14:18 GMT

> Hi,
>
> I want to use my unmanaged c++ class library from a c# client.
> my unmanaged c++ class library use polymorpism, is this polymorphism
> also exported to my c# client via PInvoke ?

I'm assuming that you're asking "Can I call a virtual function through a
pointer to a native C++ object via PInvoke?". The answer to that is no (or
at least, not directly). MC++ IJW can, however.

To call virtual functions through PInvoke you'd need to write a little
"trampoline" function and export it from your native DLL. The function
would be a non-member, taking the object pointer and all of the virtual
methods parameters as it's parameters and would perform the virtual function
call.

-cd

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yaron - 11 Jun 2005 15:22 GMT

Hi Daniel,

I will give a small scenario:
my unmanaged c++ dll receive method return a pointer to a generic message
base class but it actually can be many different concrete messages class
which derive from the generic message.
i want from my c# client to deal with the concrete message class.

can i cast down the generic message pointer to the concrete message and
access the concrete message fields from c#?

Thanks.

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Arnaud Debaene - 11 Jun 2005 17:03 GMT

> Hi Daniel,
>
[quoted text clipped - 6 lines]
> can i cast down the generic message pointer to the concrete message
> and access the concrete message fields from c#?

You'd better do it with a managed C++ (or C++/CLI) adaptation layer :
P/Invoke is well suited for C-style APIs, but it may be difficult to use it
in an OO context.

Arnaud
MVP - VC

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yaron - 11 Jun 2005 18:02 GMT

thanks a lot, it was very helpfull.

> > Hi Daniel,
> >
[quoted text clipped - 13 lines]
> Arnaud
> MVP - VC

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does PInvoke support for polymorphism ?

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