c - How to get terminal window width?

Question

I am working on embedded system using C and linux. User can connect to the device via SSH or a console serial cable. He can do this through PuTTY or Tera Term. My question is, after he is connected, how can I know his window's width? I have tried different approaches, they work if I simulate my system on a linux pc, but none of them work on the device:

1. ioctl()

   struct winsize ws;
   ioctl(..., TIOCGWINSZ, &ws); 
   

   This method works on pc, but it always returns 0 on the device.

2. tgetnum()

   setupterm((char *)0, 1, (int *)0);
   CGR_INT columns = tgetnum("co");
   

   This method works on pc, but it always returns 80x24 on the device.

3. getmaxyx()

   CGR_INT xdim;
   CGR_INT ydim;
   initscr();
   refresh();
   getmaxyx(stdscr, ydim, xdim);
   

   This method works on pc, but it always returns 0 on the device

Answer 1

I use this code to print a bunch of equals signs as a divider. Works on most boxes/terms I've tried. Not sure what devices you are talking about. Worth a try I guess ;-)

#include <termios.h>
#include <sys/ioctl.h>
#include <stdio.h>
int main(int argc, char *argv[])
{
   struct winsize ws;
   ioctl(0, TIOCGWINSZ, &ws);

   int i=0;
   for(;i<10*ws.ws_col;++i) printf("=");
   printf("
");
   return 0;
}