Hi,

I'm trying to write some app in MacRuby with CoreAudio framework.

I've notices some framework's C-function require pointer manipulation,
and for some cases, I need calculate size of C-struct, but don't know
how to get sizeof(struct Foo).

Is there any way to calculate size of C-struct in MacRuby?

For example,  to obtain available formats of audio stream,I have to
call AudioStreamGetPropertyInfo() at first.

extern OSStatus AudioStreamGetPropertyInfo(
   AudioStreamID inStream,
   UInt32 inChannel,
   AudioDevicePropertyID inPropertyID,
   UInt32*outSize,
   Boolean*outWritable);

if I specify kAudioStreamPropertyAvailableVirtualFormats as 3rd
argument(inPropertyID),
outSize gives me total required byte size for [an array of
AudioStreamRangedDescription struct] which describe available formats.

Then, AudioStreamGetProperty() will fill [an array of
AudioStreamRangedDescription struct] with available formats

extern OSStatus AudioStreamGetProperty(
   AudioStreamID inStream,
   UInt32 inChannel,
   AudioDevicePropertyID inPropertyID, //again use
kAudioStreamPropertyAvailableVirtualFormats
   UInt32*ioPropertyDataSize,
   void*outPropertyData);                      //filled by API

http://developer.apple.com/library/mac/#documentation/MusicAudio/Reference/CACoreAudioReference/AudioHardware/CompositePage.html

So, I need to write some code like

framework "CoreAudio"
def getAvailableFormats(stream, channel)

 pSize = Pointer.new("I")
 ret = AudioStreamGetPropertyInfo( stream , channel,
KAudioStreamPropertyAvailableVirtualFormats, pRequiredSize, nil)
 requiredSize = pSize[0]

 howmany = ??? # how to get reqired length of array?  in C:  howmany
= requiredSize / sizeof(  AudioStreamRangedDescription )
 pAudioStreamRangedDescription =
Pointer.new("{AudioStreamRangedDescription={AudioStreamBasicDescription=dIIIIIIII}{AudioValueRange=dd}}",
howmany)


 ret = AudioStreamGetProperty(stream, channel,
KAudioStreamPropertyAvailableVirtualFormats, pRequiredSize,
pAudioStreamRangedDescription)
 ...
end


Of course I could calculate sizeof( AudioStreamRangedDescription)
manually but it's annoying.
Is there any convenient way?
_______________________________________________
MacRuby-devel mailing list
MacRuby-devel@lists.macosforge.org
http://lists.macosforge.org/mailman/listinfo.cgi/macruby-devel