Advanced Programming in the UNIX® Environment

ptg10805159

Section 18.8 Line Control Functions 693

The four baud rate functions exist to insulate applications from differences in the

way that implementations represent baud rates in thetermiosstructure. Linux and

BSD-derived platforms tend to storebaud rates as numeric values equal to the rates

(i.e., 9,600 baud is stored as the value 9,600), whereas System V–derived platforms (such

as Solaris) tend to encode the baud rate in a bitmask. The speed values we get from the

cfget functions and pass to the cfset functions areuntranslated from their

representation as they arestored in thetermiosstructure.

18.8 Line Control Functions

The following four functions provide line control capability for terminal devices. All

four requirethatfdrefer to a terminal device; otherwise,−1 is returned witherrnoset

toENOTTY.

#include <termios.h>

int tcdrain(intfd);

int tcflow(intfd,intaction);

int tcflush(intfd,intqueue);

int tcsendbreak(intfd,intduration);

All four return: 0 if OK,−1 on error

Thetcdrainfunction waits for all output to be transmitted. Thetcflowfunction

gives us control over both input and output flow control. Theactionargument must be

one of the following four values:

TCOOFF Output is suspended.

TCOON Output that was previously suspended is restarted.

TCIOFF The system transmits a STOP character,which should cause the terminal

device to stop sending data.

TCION The system transmits a STARTcharacter,which should cause the terminal

device to resume sending data.

Thetcflushfunction lets us flush (throw away) either the input buffer (data that

has been received by the terminal driver,which we have not read) or the output buffer

(data that we have written, which has not yet been transmitted). Thequeueargument

must be one of the following three constants:

TCIFLUSH The input queue is flushed.

TCOFLUSH The output queue is flushed.

TCIOFLUSH Both the input and the output queues areflushed.