snd_ctl_callbacks_t

Control callback functions

Synopsis:

typedef struct snd_ctl_callbacks {
    void *private_data; /* should be used by an application */
    void (*rebuild) (void *private_data);
    void (*xswitch) (void *private_data, int cmd,
                     int iface, snd_switch_list_item_t *item);
    void *reserved[29]; /* reserved for future use - must be NULL!!! */
} snd_ctl_callbacks_t;

Description:

Use the snd_ctl_callbacks_t structure to define the callback functions that you need to handle control events. Pass a pointer to an instance of this structure to snd_ctl_read().

The members of the snd_ctl_callbacks_t structure include:

• private_data, a pointer to arbitrary data that you want to pass to the callbacks
• pointers to the callbacks, which are described below.

---

Make sure that you zero-fill any members that you aren't interested in. You can zero-fill the entire snd_ctl_callbacks_t structure if you aren't interested in tracking any of these events.

---

rebuild callback

The rebuild callback is called whenever the control device is rebuilt. Its only argument is the private_data that you specified in this structure.

xswitch callback

The xswitch callback is called whenever a switch changes. Its arguments are:

private_data

A pointer to the arbitrary data that you specified in this structure.

cmd

One of:

• SND_CTL_READ_SWITCH_VALUE
• SND_CTL_READ_SWITCH_CHANGE
• SND_CTL_READ_SWITCH_ADD
• SND_CTL_READ_SWITCH_REMOVE

iface

The device interface the switch is natively associated with. The possible values are (from <sys/asound.h>):

• SND_CTL_IFACE_CONTROL
• SND_CTL_IFACE_MIXER
• SND_CTL_IFACE_PCM_PLAYBACK
• SND_CTL_IFACE_PCM_CAPTURE

item

A pointer to a snd_switch_list_item_t structure that identifies the specific switch that's been changed. This structure has only a name member.

Classification:

QNX Neutrino

See also:

snd_ctl_read().