#include <callback.h>
If the seek requirement for an interface is optional, you can signify that a data sorce is not seekable by setting the seek field to NULL. 
| Public Attributes | |
| FLAC__IOCallback_Read | read | 
| FLAC__IOCallback_Write | write | 
| FLAC__IOCallback_Seek | seek | 
| FLAC__IOCallback_Tell | tell | 
| FLAC__IOCallback_Eof | eof | 
| FLAC__IOCallback_Close | close |