I wrote a proram which call tcflow(fd,TCOOFF) to suspend output and then call tcflow(fd, TCOON) to restore output in LINUX. fd is stdout's fd. the program suspended and I can't do any thing at the terminal to make it active. By gdb,I find process is suspending at tcflow(fd,TCOOFF).
What is the reason and how solve it?
Thanks for help.

#include <termios.h>
#include <unistd.h>
#include <stdlib.h>
char buf[]="Hello!";
int a[]={1,2,3,4,5,6,7,8,9,0};
int main()
{
int fd;
fd=fileno(stdout);
write(fd,buf,sizeof(buf));
tctrain(fd);
tcflow(fd, TCOOFF);/* process stop at here */
write(fd, a, 10);
tcflush(fd,TCIOFLUSH);
tcflow(fd,TCOON);
}

it only seems to lock up when it is written to while it is disabled. is this you intention to write while it is off?

thanks you help.
I just want to see what will happen while is off. Now I see WRITE will suspend process while transmission is disabled. This situation makes terminal unable working.

And there is another question about the code below:

#include <stdio.h>
#include <unistd.h>
#include <termios.h>
int main(void)
{
int fd;
fd = fileno(stdout);
write (fd,"Example of line control functions \n",34);
tcdrain (fd);
fprintf (stdout, "this line is delayed "); /* ??? */
tcflow(fd, TCOOFF);
tcflush(fd, TCIOFLUSH);
tcflow (fd, TCOON);
write(fd,"restart the output\n",20);
}

I run the program in LINUX and get result as below:

$a.out
Example of line control functions restart the output
this line is delayed $

It seems that the line outputed by fprintf should be
flushed by tcflush(), but it is not. why?

Maybe I am not well understand the mean of tcflush or the way of terminal i/o.