snd_ctl_read()
Read pending control events
Synopsis:
#include <sys/asoundlib.h>
int snd_ctl_read( snd_ctl_t *handle,
snd_ctl_callbacks_t *callbacks );
Arguments:
- handle
- The handle for the control connection to the card. This must be a handle created by snd_ctl_open().
- callbacks
- A pointer to a snd_ctl_callbacks_t structure that defines the callbacks for the events.
Library:
libasound.so
Use the -l asound option with qcc to link against this library.
Description:
The snd_ctl_read() function reads pending control events from the control handle. As each event is read, the list of callbacks is checked for a handler for this event. If a match is found, the callback is invoked. This function is usually called on the return of the select() library call (see the QNX Neutrino C Library Reference).
By default, events are disabled and an application must enable them using snd_ctl_set_filter(). Use snd_ctl_set_filter() and snd_ctl_get_filter() to tell io-audio which events you are interested in monitoring, handling, or both.
Returns:
The number of events read from the handle, or a negative value on error.
Errors:
- -EBADF
- Invalid file descriptor. Your handle may be corrupt.
- -EINTR
- The read operation was interrupted by a signal, and either no data was transferred, or the resource manager responsible for that file doesn't report partial transfers.
- -EIO
- An event I/O error occurred.
Classification:
QNX Neutrino
| Safety: | |
|---|---|
| Cancellation point | No |
| Interrupt handler | No |
| Signal handler | Yes |
| Thread | Yes |