snd_pcm_query_chmaps()

Get a list of the available channel mappings for a PCM stream

Synopsis:

#include <sys/asoundlib.h>

snd_pcm_chmap_query_t **snd_pcm_query_chmaps( snd_pcm_t *pcm );

Arguments:

pcm
The handle for the PCM device, which you must have opened by calling snd_pcm_open_name(), snd_pcm_open(), or snd_pcm_open_preferred().

Library:

libasound.so

Use the -l asound option to qcc to link against this library.

Description:

The snd_pcm_query_chmaps() function returns a list of the available channel mappings for a PCM stream. To free this list, call snd_pcm_free_chmaps().

Returns:

A pointer to an array of snd_pcm_chmap_query_t structures that describe the mappings, or NULL if no mappings are available or an error occurred (errno is set).

Errors:

EINVAL
The value of pcm is NULL.
ENOMEM
Not enough memory was available.

Examples:

snd_pcm_chmap_query_t **chmaps;
snd_pcm_chmap_t *chmap;
int i, j;

/* Check available channel maps */
printf("Get all available channel maps...\n");
if ((chmaps = snd_pcm_query_chmaps(pcm_handle)) == NULL)
{
    fprintf(stderr, "snd_pcm_query_chmaps failed: %s\n", snd_strerror(rtn));
    return -1;
}

for (i=0; chmaps[i] != NULL; i++)
{
    printf("chmaps[%d]:\n", i);
    printf("Map Type = %d\n", chmaps[i]->type);
    printf("Number of channels = %d\n", chmaps[i]->map.channels);
    for(j = 0; j < chmaps[i]->map.channels; j++)
        printf("\tchmaps[%d].pos[%d] = %d\n", i, j, chmaps[i]->map.pos[j]);
}

snd_pcm_free_chmaps(chmaps);

Classification:

QNX Neutrino

Safety:  
Cancellation point No
Interrupt handler No
Signal handler Yes
Thread Read the Caveats

Caveats:

This function isn't thread-safe if pcm (snd_pcm_t) is used across multiple threads.