Transfer PCM data from the capture channel


#include <sys/asoundlib.h>

ssize_t snd_pcm_read( snd_pcm_t *handle, 
                      void *buffer, 
                      size_t size );


The handle for the PCM device, which you must have opened by calling snd_pcm_open() or snd_pcm_open_preferred().
A pointer to a buffer in which snd_pcm_read() can store the data that it reads.
The size of the buffer, in bytes.



The snd_pcm_read() function reads samples from the device, which must be in the proper format specified by snd_pcm_channel_prepare() or snd_pcm_capture_prepare().

This function may suspend the client application if blocking mode is active (see snd_pcm_nonblock_mode()) and no data is available for read.

When the subdevice is in blocking mode (SND_PCM_MODE_BLOCK), then the number of read bytes must fulfill the N × fragment-size expression, where N > 0.

If the stream format is noninterleaved (i.e. the interleave member of the snd_pcm_format_t structure isn't set), then the driver returns data that's separated to single voice blocks encapsulated to fragments. For example, imagine you have two voices, and the fragment size is 512 bytes. The number of bytes per one voice is 256. The driver returns the first 256 bytes that contain samples for the first voice, and the second 256 bytes from the fragment size that contains samples for the second voice.


A positive value that represents the number of bytes that were successfully read from the device if the capture was successful, or a negative value if an error occurred.


The subdevice has no data available.
Failed to copy data.
Invalid handle; data pointer is NULL but size isn't zero or is negative.
The channel isn't in the prepared or running state.


QNX Neutrino

Cancellation point No
Interrupt handler No
Signal handler Yes
Thread Yes

See also:

snd_pcm_capture_prepare(), snd_pcm_channel_prepare(), snd_pcm_format_t, snd_pcm_plugin_read(), snd_pcm_write()