The Linux Programming Interface

1320 Chapter 62

Listing 62-5: Monitoring changes in the terminal window size

–––––––––––––––––––––––––––––––––––––––––––––––––––––– tty/demo_SIGWINCH.c

#include <signal.h>

#include <termios.h>

#include <sys/ioctl.h>

#include "tlpi_hdr.h"

static void

sigwinchHandler(int sig)

{

}

int

main(int argc, char *argv[])

{

struct winsize ws;

struct sigaction sa;

sigemptyset(&sa.sa_mask);

sa.sa_flags = 0;

sa.sa_handler = sigwinchHandler;

if (sigaction(SIGWINCH, &sa, NULL) == -1)

errExit("sigaction");

for (;;) {

pause(); /* Wait for SIGWINCH signal */

if (ioctl(STDIN_FILENO, TIOCGWINSZ, &ws) == -1)

errExit("ioctl");

printf("Caught SIGWINCH, new window size: "

"%d rows * %d columns\n", ws.ws_row, ws.ws_col);

}

}

–––––––––––––––––––––––––––––––––––––––––––––––––––––– tty/demo_SIGWINCH.c

It is also possible to change the terminal driver’s notion of the window size by pass-

ing an initialized winsize structure in an ioctl() TIOCSWINSZ operation:

ws.ws_row = 40;

ws.ws_col = 100;

if (ioctl(fd, TIOCSWINSZ, &ws) == -1)

errExit("ioctl");

If the new values in the winsize structure differ from the terminal driver’s current

notion of the terminal window size, two things happen:

z The terminal driver data structures are updated using the values supplied in

the ws argument.

z A SIGWINCH signal is sent to the foreground process group of the terminal.