[LAD] jack and c++

cal cal at graggrag.com
Mon Nov 10 09:10:00 UTC 2008

Malte Steiner wrote:
> For a new audio application I need to code a JACK client with C++. So
> far I did it only with C and have a problem with giving the pointer to
> the callback process function, which is a method now. So what is the
> best performing solution? Is a delegate function a good idea, being
> static and triggering the method in the objectinstance?

No idea what the best solution might be, but here's an approach I've used...

class AudioOutputJACK
       [ ... ]
       static int ProcessJackCallback(jack_nframes_t nframes, void* arg);

And in the class initialisation,

   if ((chk = jack_set_process_callback(jack_client, ProcessJackCallback,
   { ... }

And the callback function ...

int AudioOutputJACK::ProcessJackCallback(jack_nframes_t nframes, void* arg)
   AudioOutputJACK* audJ = static_cast<AudioOutputJACK*>(arg);
   // then stuff like ...
   size_t bytes_requested = nframes * audJ->jack_frame_bytes;
   size_t bytes_read = jack_ringbuffer_read(audJ->ringbuffJ,
   etc ...

cheers, Cal

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