note for tcflush

tcflush

int tcflush(int fd, int queue_selector);

tcflush() discards data written to the object referred to by fd but not transmitted, or data received but not read, depending on the value of queue_selector. 

TCIFLUSH

flushes data received but nor read.

TCOFLUSH

flushes data written but not transmitted.

TCIOFLUSH

flushes both data received but not read, and data written but not transmitted.