NAME

tcflow - suspend or restart the transmission or reception of data

 SYNOPSIS

#include <termios.h>

int tcflow(int fildes, int action);

 DESCRIPTION

The tcflow() function suspends transmission or reception of data on the object referred to by fildes, depending on the value of action. The fildes argument is an open file descriptor associated with a terminal.

• If action is TCOOFF, output is suspended.

• If action is TCOON, suspended output is restarted.

• If action is TCIOFF, the system transmits a STOP character, which is intended to cause the terminal device to stop transmitting data to the system.

• If action is TCION, the system transmits a START character, which is intended to cause the terminal device to start transmitting data to the system.

The default on the opening of a terminal file is that neither its input nor its output are suspended.

Attempts to use tcflow() from a process which is a member of a background process group on a fildes associated with its controlling terminal, will cause the process group to be sent a SIGTTOU signal. If the calling process is blocking or ignoring SIGTTOU signals, the process is allowed to perform the operation, and no signal is sent.

 RETURN VALUE

Upon successful completion, 0 is returned. Otherwise, -1 is returned and errno is set to indicate the error.

 ERRORS

The tcflow() function will fail if:

[EBADF]

The fildes argument is not a valid file descriptor.

[EINVAL]

The action argument is not a supported value.

[ENOTTY]

The file associated with fildes is not a terminal.

The tcflow() function may fail if:

[EIO]

The process group of the writing process is orphaned, and the writing process is not ignoring or blocking SIGTTOU.

 EXAMPLES

None.

 APPLICATION USAGE

None.

 FUTURE DIRECTIONS

In the ISO POSIX-1 standard, the possibility of an [EIO] error occurring is described in XBD specification, Terminal Access Control , but it is not mentioned in the tcflow() interface definition. It has become clear that this omission was unintended, so it is likely that the [EIO] error will be re-classified as a "will fail" in a future issue of the POSIX standard.

 SEE ALSO

tcsendbreak(), <termios.h>, <unistd.h>, the XBD specification, General Terminal Interface .

DERIVATION

Derived from the POSIX.1-1988 standard.