ul_byte * dst,
size_t * retr_len
dst The buffer to receive bytes.
len The length of the buffer.
retr_len An output parameter. The actual number of bytes returned.
Retrieves the current value into a binary buffer, casting as required If the buffer is too small, then the value is truncated.
Up to len bytes are copied to the given buffer. The number of bytes actually copied is returned in retr_len.