[MacRuby-devel] MacRuby equivalent to C sizeof(struct Foo)

[kyossi]

Hi,

Thanks for help.

OK, I've created a new ticket as below.
https://www.macruby.org/trac/ticket/1080

Thanks&Regards.

kyossi

>Hi,

>There is no way to do that for now. Could you file a ticket? I will introduce #size on C structs classes.

>NSRect.size in MacRuby would be the same as sizeof(NSRect) in C.

>Laurent


On Dec 24, 2010, at 12:19 PM, kyossi wrote:

> 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?
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