tcflow

tcflow

Controls the Flow of Data to a Terminal

Portability: POSIX.1 conforming

SYNOPSIS
DESCRIPTION
RETURN VALUE
EXAMPLE
RELATED FUNCTIONS

SYNOPSIS

#include <termios.h>

int tcflow(int fileDescriptor, int action);

DESCRIPTION

tcflow controls the flow of data to and from a terminal device. Because USS OS/390 supports only pseudo-terminals, tcflow affects only the flow of data between the OMVS TSO command and user programs. It does not directly affect transmission to and from a user's 3270 terminal.

The arguments to tcflow are:

fileDescriptor

is a file descriptor that refers to a terminal device.

action

is a symbolic constant that controls the action of tcflow . The values for action are defined in <termios.h> and can be any of the following:

`TCOOFF`	suspends output to the terminal.
`TCOON`	restarts suspended output to a terminal.
`TCIOFF`	transmits a `STOP` character to a terminal. This should stop further transmission of data from the terminal.
`TCION`	transmits a `START` character to a terminal. This should restart the transmission of data from the terminal.

If tcflow is called from a background process, with a file descriptor that refers to the controlling terminal for the process, a SIGTTOU signal may be generated. This will cause the function call to be unsuccessful, returning a -1 . If SIGTTOU is blocked, the function call proceeds normally.

RETURN VALUE

tcflow returns a 0 if successful and a -1 if unsuccessful.

EXAMPLE

The following example illustrates the use of tcflow to suspend data transmission:

#include <sys/types.h>
#include <termios.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

main()
{
   int ttyDevice = STDOUT_FILENO;

   /* Make sure file descriptor is for a TTY device,               */
   if ( ! isatty(ttyDevice) ) {
      printf("Not a TTY device.n");
      return(EXIT_FAILURE);
   }

      /* Suspend and resume data transmission,                        */
   else {
      printf("About to suspend data transmission for 5 seconds.n");
      if (tcflow(ttyDevice, TCOOFF) != 0) {
         perror("tcflow error");
         exit(EXIT_FAILURE);
      }
      sleep(5);
      if (tcflow(ttyDevice, TCOON) == 0)
         printf("Data transmisiion suspended and resumed.n");
      else {  /* We turned it off, and now we can't turn it back on!  */
         perror("tcflow error");  /* probably message will be lost    */
         abort();
   }
   return(EXIT_SUCCESS);
}

RELATED FUNCTIONS

tcdrain , tcflush

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