tcflow -- Controls the Flow of Data to a Terminal

SYNOPSIS

 #include <termios.h>

 int tcflow(int fileDescriptor, int action);

DESCRIPTION

tcflow controls the flow of data to and from a terminal device. Because OpenEdition MVS 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