Getting terminal width in C?

Question

I've been looking for a way to get the terminal width from within my C program. What I keep coming up with is something along the lines of:

#include <sys/ioctl.h> #include <stdio.h>  int main (void) {     struct ttysize ts;     ioctl(0, TIOCGSIZE, &ts);      printf ("lines %d\n", ts.ts_lines);     printf ("columns %d\n", ts.ts_cols); } 

But everytime I try that I get

austin@:~$ gcc test.c -o test test.c: In function ‘main’: test.c:6: error: storage size of ‘ts’ isn’t known test.c:7: error: ‘TIOCGSIZE’ undeclared (first use in this function) test.c:7: error: (Each undeclared identifier is reported only once test.c:7: error: for each function it appears in.) 

Is this the best way to do this, or is there a better way? If not how can I get this to work?

EDIT: fixed code is

#include <sys/ioctl.h> #include <stdio.h>  int main (void) {     struct winsize w;     ioctl(0, TIOCGWINSZ, &w);      printf ("lines %d\n", w.ws_row);     printf ("columns %d\n", w.ws_col);     return 0; } 

Answer 1

Have you considered using getenv() ? It allows you to get the system's environment variables which contain the terminals columns and lines.

Alternatively using your method, if you want to see what the kernel sees as the terminal size (better in case terminal is resized), you would need to use TIOCGWINSZ, as opposed to your TIOCGSIZE, like so:

struct winsize w; ioctl(STDOUT_FILENO, TIOCGWINSZ, &w); 

and the full code:

#include <sys/ioctl.h> #include <stdio.h> #include <unistd.h>  int main (int argc, char **argv) {     struct winsize w;     ioctl(STDOUT_FILENO, TIOCGWINSZ, &w);      printf ("lines %d\n", w.ws_row);     printf ("columns %d\n", w.ws_col);     return 0;  // make sure your main returns int } 

Answer 2

This example is a bit on the lengthy side, but I believe it's the most portable way of detecting the terminal dimensions. This also handles resize events.

As tim and rlbond suggests, I'm using ncurses. It guarantees a great improvement in terminal compatability as compared to reading environment variables directly.

#include <ncurses.h> #include <string.h> #include <signal.h>  // SIGWINCH is called when the window is resized. void handle_winch(int sig){   signal(SIGWINCH, SIG_IGN);    // Reinitialize the window to update data structures.   endwin();   initscr();   refresh();   clear();    char tmp[128];   sprintf(tmp, "%dx%d", COLS, LINES);    // Approximate the center   int x = COLS / 2 - strlen(tmp) / 2;   int y = LINES / 2 - 1;    mvaddstr(y, x, tmp);   refresh();    signal(SIGWINCH, handle_winch); }  int main(int argc, char *argv[]){   initscr();   // COLS/LINES are now set    signal(SIGWINCH, handle_winch);    while(getch() != 27){     /* Nada */   }    endwin();    return(0); }