[alsa-devel] Alsa Callbacks and C++ classes

Reuben Martin reuben.m at gmail.com
Tue Apr 22 02:49:54 CEST 2008

Back on Monday 21 April 2008, Takashi Iwai was like:
> At Sun, 20 Apr 2008 21:28:25 -0500,
> Reuben Martin wrote:
> > Hello all,
> >
> > I have an AES32 sound card that I am trying to write a general control
> > interface for using qt4. I'm wanting to register callbacks so that the
> > interface will reflect changes made by other apps. Now I'm not entirely
> > up to speed on the API, but from what I can gather, the callback can be
> > registered to call a regular function, or to change a public class
> > variable.
> >
> > Since I decided to use qt4, everything is in classes. Is there any way to
> > have the callback trigger a public class function? I guess I don't
> > understand why you would want to use a public variable instead. Wouldn't
> > you have to set up a means within the class to continually pole the
> > variable to see if it has been changed? Or can the option to call a
> > regular function be used to call a public class function as well?
> Well, which callback do you have in your mind?  A bit more
> specificically please...

Sorry about that. The callbacks I was referring to are mixer callbacks, 
specifically snd_mixer_set_callback and snd_mixer_set_callback_private.

I wrote "public" in my original post, when I meant "private". And now that I'm 
looking at it I think I may have misunderstood what 
snd_mixer_set_callback_private was for.

Anyway, I'm just wondering if it's possible (while maintaining sanity) to 
interface one of these mixer callbacks with a class public function. Or if 
there is a better means to get feedback when changes are made to one of the 
simple mixer elements.


More information about the Alsa-devel mailing list