[gmpi] Re: low level API - Abstract Factory summary
- From: "B.J. Buchalter" <bj@xxxxxxxxxx>
- To: "gmpi@xxxxxxxxxxxxx" <gmpi@xxxxxxxxxxxxx>
- Date: Thu, 10 Feb 2005 14:58:16 -0500
on 2/10/05 2:38 PM, Jeff McClintock at jeffmcc@xxxxxxxxxx wrote:
> As to C++ compilers supporting COM. I suggest GMPI uses plain C at the
> lowest level (with a C++ wrapper on top).
> COM interfaces declared in C are 100% ansii C, and compatible with
> *all* compilers. It's a bit more long-winded, but thats C for you...
>
> // INTERFACES (abstract base classes)
> typedef struct
> {
> struct IFooVtbl *IGMPI_PluginVtbl;
> } IGMPI_Plugin;
>
> typedef struct
> {
> // IUnknown methods
> GMPI_RESULT (*QueryInterface) (IGMPI_Plugin *, const
> _GMPI_GUID, void **);
> unsigned long (*AddRef) (IGMPI_Plugin *);
> unsigned long (*Release) (IGMPI_Plugin *);
>
> // IGMPI_Plugin methods
> unsigned long (*Placeholder1) (IGMPI_Plugin *, int);
> unsigned long (*Placeholder2) (IGMPI_Plugin *, int *);
> } IGMPI_PluginVtbl;
Agree, but note that the vtable format is platform dependent. On Mac OS X
the first member of the vtable is a reserved void* (see
<CoreFoundation/CFPlugIn.h>), and is apparently part of Microsoft's binary
run-time spec for COM on MacOS. So this specification needs to be:
typedef struct
{
#ifdef MACOSX // or maybe just MACOS
void *_reserved; /* The _reserved field is part of the Microsoft
COM binary standard on Macintosh. */
#endif
// IUnknown methods
GMPI_RESULT (*QueryInterface) (IGMPI_Plugin *,
const _GMPI_GUID, void **);
unsigned long (*AddRef) (IGMPI_Plugin *);
unsigned long (*Release) (IGMPI_Plugin *);
// IGMPI_Plugin methods
unsigned long (*Placeholder1) (IGMPI_Plugin *, int);
unsigned long (*Placeholder2) (IGMPI_Plugin *, int *);
} IGMPI_PluginVtbl;
Best regards,
B.J. Buchalter
Metric Halo
5 Donovan Drive
Hopewell Junction, NY 12533 USA
tel +1 845 223-6112
fax +1 603 250-2451
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