Dennis Ruffer wrote:
>
> On Nov 29, 2008, at 3:42 AM, Anton Ertl wrote:
> > Dennis Ruffer wrote:
> >>
> >> Here's yet another puzzle for the interface semantics:
> >>
> >> err = (*iodev)->QueryInterface(iodev, CFUUIDGetUUIDBytes
> >> (kIOUSBDeviceInterfaceID), (LPVOID)&dev);
> >>
> >> Does this have anything to do with the function pointers described in
> >> the docs, or is this something else entirely?
> >
> > Yes, this looks like a call through a function pointer.
>
> Thanks for the answers Jack and Anton, here's what I've got so far:
>
> err = (*dev)->Release(dev);
>
> becomes:
>
> \c typedef long (* func1)(void*);
> \c #define call_func1(par1,fptr) ((func1)fptr)(par1)
> c-function call_func1 call_func1 a func -- n
>
> begin-structure IUNKNOWN_C_GUTS
> field: reserved
> field: QueryInterface \ a a a -- n
> field: AddRef \ a -- n
> field: Release \ a -- n
> end-structure
>
> dev @ dup @ Release @ call_func1 .
>
> However, with QueryInterface, I need to figure out what
> CFUUIDGetUUIDBytes is doing
>
> It is defined as:
>
> typedef struct {
...
> } CFUUIDBytes;
> /* The CFUUIDBytes struct is a 128-bit struct that contains the
> raw UUID. A CFUUIDRef can provide such a struct from the
> CFUUIDGetUUIDBytes() function. This struct is suitable for
> passing to APIs that expect a raw UUID.
> */
>
> CFUUIDBytes CFUUIDGetUUIDBytes(CFUUIDRef uuid);
>
> However, I can't figure out any thing to put in the return value to
> prevent errors.
Structs as return values (or as parameters) are not yet supported by
the libcc interface, but one can work around that (see below).
> c-function CFUUIDGetUUIDBytes CFUUIDGetUUIDBytes a -- a
>
> gives me:
>
> /Users/druffer/.gforth/libcc-tmp/gforth_c_103DF4C.c:11: error:
> aggregate value used where an integer was expected
>
> What is an aggregate return value?
A struct or a union.
There are several workarounds possible.
- If you always want to use QueryInterface with the CFUUIDGetUUIDBytes
call as second parameter, just put the call in the macro for the
QueryInterface call.
- OTOH, if you want to do the CFUUIDGetUUIDBytes call at the Forth
level, you have to work around the inability to return a struct and
around the inability to pass a struct. A way to do this is to create
your own buffer for a temporary CFUUIDBytes struct, and pass a pointer
to this struct to a CFUUIDGetUUIDBytes macro and a QueryInterface
macro. These macros would have to do any dereferencing or somesuch
themselves, e.g.:
\c #define CFUUIDGetUUIDBytes1(uuid,res) (*(CFUUIDBytes *)(res) =
CFUUIDGetUUIDBytes((CFUUIDRef)uuid)
c-function CFUUIDGetUUIDBytes1 CFUUIDGetUUIDBytes1 a a -- void
\c #define call_QueryInterface(f,x,y,z) (((functype)f)(x,*(CFUUIDBytes *)y,z))
c-function call-QueryInterface func a a a -- n
and call it like:
create CFUUIDBytesbuf 16 allot
uuid1 CFUUIDBytesbuf CFUUIDGetUUIDBytes1
iodev1 QueryInterface @ iodev1 CFUUIDBytesbuf devbuf call-QueryInterface
or something along these lines.
- anton
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