Any way to access a C++ DLL?

[Steve Horne]

On Wed, 06 Sep 2006 13:03:40 +0200, mike <vertex at gmx.at> wrote:

>Is there any way to access a C++ DLL (precisely: a VST plugin - for those  
>who don't know: VST is a plugin API for virtual synthesizers, audio/midi  
>effects, etc.) from D?

I'm a newb, but I can still say yes - in principle.


Worst case, you write an adaptor lib in C++ which provides a C level
API. D can easily call that. On the C level, you see functions that
take 'handles' as parameters.

It's a lot like the Windows APIs - those window and device context
handles are actually object pointers and, very likely, those C-like
function calls use an underlying C++-style virtual function call in
order to resolve what kind of window/device context/whatever they are
dealing with.

I haven't dealt with VST plugins, but for the main plugin mechanism I
have used, there is a single exported function in the DLL. This is
normally accessed through GetProcAddress, and when called it provides
an object which is used as a kind of 'factory' for API objects.

Mapping all of that to a C-compatible adaptor lib would be a pain, but
not difficult as such. Just hassle.

You could, of course, use SWIG. AFAIK it can't generate D wrappers
yet, but it can generate an XML description of a C++ API which you
could then translate to a D wrapper using XSLT. Of course this might
take some time and fiddling around.


Far better case - perhaps VST uses COM? After all, there aren't any
big overheads to using COM, providing the interfaces are provided by a
local DLL. All basic COM does is allow an executable or DLL to call
create objects and call interfaces defined in another DLL. The calls
are just C++-style virtual function calls through an interface object
pointer.

I believe D has built-in support for COM, making it easier to program
COM in D than in C++, though I haven't used it.

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