snd_ctl_mixer_switch_list()
Get the number and names of control switches for the mixer
Synopsis:
#include <sys/asoundlib.h >
int snd_ctl_mixer_switch_list( snd_ctl_t *handle,
int dev, snd_switch_list_t *list );
Arguments:
- handle
- The handle for the control device. This must have been created by snd_ctl_open().
- dev
- The mixer device the switches apply to.
- list
- A pointer to a snd_switch_list_t structure that snd_ctl_mixer_switch_list() fills with information about the switch.
Library:
libasound.so
Use the -l asound option with qcc to link against this library.
Description:
The snd_ctl_mixer_switch_list() function uses the control device handle to fill the given snd_switch_list_t structure with the number of switches for the mixer specified. It also fills in the array of switches pointed to by pswitches to a limit of switches_size. Before calling snd_mixer_groups(), set the members of the snd_switch_list_t as follows:
- pswitches
- This pointer must be NULL or point to a valid storage location for the switches (i.e., an array of snd_switch_list_item_t structures).
- switches_size
- The size of the pswitches storage location in sizeof( snd_switch_list_item_t ) units (i.e., the number of entries in the array).
On a successful return, the snd_ctl_mixer_switch_list() function will fill in these members:
- switches
The number of switches retrieved into the pswitch local storage. Read only.
- switches_over
The number of switches that could not be retrieved due to the size constraints of the pswitches local storage. Read only.
Returns:
Zero on success, or a negative value if an error occurs.
Errors:
- -EINVAL
- Invalid handle argument.
Classification:
QNX Neutrino
| Safety: | |
|---|---|
| Cancellation point | No |
| Signal handler | Yes |
| Thread | Yes |
Caveats:
The switch struct must be initialized to a known state before making the call; use memset() to set the struct to zero, and then set the name member to specify which switch to read.