Display timer same time as input

This is a discussion on Display timer same time as input within the Linux Programming forums, part of the Platform Specific Boards category; Hi all, I want to display a timer the same time I am accepting input in a curses(3) program. I ...

  1. #1
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    Display timer same time as input

    Hi all,

    I want to display a timer the same time I am accepting input in a
    curses(3) program. I am using alarm(3) as my timer. The problem is that
    the timer is not updated when I am accepting input; it is updated after I
    press a key. Here is the code:

    Code:
    #include <ctype.h>
    #include <curses.h>
    #include <unistd.h>
    #include <signal.h>
    #include <stdlib.h>
    
    static char _hour = 0, _min = 0, _sec = 0;
    
    void disp_timer()
    {
      char sprintf_buf[10];
    
      sprintf(sprintf_buf, "%02i:%02i:%02i", _hour, _min, _sec);
      mvaddstr(3, 3, sprintf_buf);
    }
    
    void alarm_handler(int sig)
    {
      _sec++;
         
      if(_sec == 60)
      {
        _sec = 0;
        _min++;
      
        if(_min == 60)
        {
          _min = 0;
         _hour++;
        }   
      }
    
      disp_timer();
      signal(SIGALRM, alarm_handler); /* watch on alarm again */
      alarm(1);
    }
    
    void finish(int sig)
    {
      endwin();
      exit(0);
    }
    
    int main()
    {
      int i;
      char again, ch;
      char sprintf_buf[15];
    
      initscr();
      noecho();
      cbreak();
      disp_timer();
      signal(SIGINT, finish); /* ^C exits and cleans up program */
      signal(SIGALRM, alarm_handler);
      alarm(1);
    
      again = 1;
    
      do
      {
        for(i = 0; i < 10; i++)
        {
          clear();
          disp_timer();
          sprintf(sprintf_buf, "Question %i: ", i);
          mvaddstr(0, 0, sprintf_buf);
          getch();
          sprintf(sprintf_buf, "Answer: %i", i);
          mvaddstr(1, 0, sprintf_buf);
          getch();
        }
    
        clear();
        disp_timer();
        mvaddstr(0, 0, "Again (y/n)? ");
        ch = getch();
    
        if(toupper(ch) == 'N')
          again = 0;
      } while(again);
    
      finish(0);
    
      return 0;
    }
    Any ideas?

    Thanks,
    Yasir

  2. #2
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    Anyone?

    I played around with this last night. I forked a child process that would only display the timer. Although the timer was being incremented, nothing was being displayed on the screen. Then I got the idea of using another window to display the timer. I still can't get it to work, but I think I'm close.

    Code:
    #include <ctype.h>
    #include <curses.h>
    #include <unistd.h>
    #include <signal.h>
    #include <stdlib.h>
    #include <sys/wait.h>
    
    char _hour = 0, _min = 0, _sec = 0;
    WINDOW *timer_win;
    
    void disp_timer()
    {
      char sprintf_buf[10];
    
      sprintf(sprintf_buf, "%02i:%02i:%02i", _hour, _min, _sec);
      mvwaddstr(timer_win, 3, 3, sprintf_buf);
    }
    
    void alarm_handler(int sig)
    {
      _sec++;
         
      if(_sec == 60)
      {
        _sec = 0;
        _min++;
      
        if(_min == 60)
        {
          _min = 0;
         _hour++;
        }   
      }
    
      disp_timer();
      signal(SIGALRM, alarm_handler); /* watch on alarm again */
      alarm(1);
    }
    
    void finish(int sig)
    {
      endwin();
      exit(0);
    }
    
    int main()
    {
      int i;
      char again, ch;
      char sprintf_buf[15];
    
      initscr();
      noecho();
      cbreak();
    
      timer_win = newwin(1, 10, 3, 3);
    
      disp_timer();
      signal(SIGINT, finish); /* ^C exits and cleans up program */
      signal(SIGALRM, alarm_handler);
      alarm(1);
    
      again = 1;
    
      do
      {
        for(i = 0; i < 10; i++)
        {
          clear(); /* should clear only stdscr, not timer_win */
          sprintf(sprintf_buf, "Question %i: ", i);
          mvaddstr(0, 0, sprintf_buf);
          getch();
          sprintf(sprintf_buf, "Answer: %i", i);
          mvaddstr(1, 0, sprintf_buf);
          getch();
        }
    
        clear();
        mvaddstr(0, 0, "Again (y/n)? ");
        ch = getch();
    
        if(toupper(ch) == 'N')
          again = 0;
      } while(again);
    
      finish(0);
    
      return 0;
    }

  3. #3
    Sr. Software Engineer filker0's Avatar
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    mvaddstr(3X) does not update the display -- you must call refresh(3X) or wrefresh(3X) to update the actual display in your alarm handler.

    I hope this helps.

    [edit]A subprocess has the problem that it's probably not dealing with the same curses screen buffer, so it will wipe out anything that's on the display. A separate thread would work, assuming that the curses library is thread safe (I don't know off the top of my head.)[/edit]
    Last edited by filker0; 12-28-2005 at 09:52 AM. Reason: Update to reflect second posting
    Insert obnoxious but pithy remark here

  4. #4
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    Ok, I'm getting closer. However, here's the problem: when I call getch(), it refreshes the main window, thus placing the main window on top of timer_win. If the alarm goes off, timer_win will be displayed, but since the alarm is happening asynchronously of getch(), the timer disappears until the alarm goes off again. Also, the cursor jumps around. Is there a way to get around this? By the way, when I had created two process, the main window displayed everything correctly, but timer_win was never displayed. I did the fork after the call to initscr(). I even tried doing dupwin().
    Code:
    #include <ctype.h>
    #include <curses.h>
    #include <unistd.h>
    #include <signal.h>
    #include <stdlib.h>
    #include <sys/wait.h>
    
    char _hour = 0, _min = 0, _sec = 0;
    WINDOW *timer_win;
    
    void disp_timer()
    {
      mvwprintw(timer_win, 0, 0, "%02i:%02i:%02i", _hour, _min, _sec);
      wrefresh(timer_win);
    }
    
    void alarm_handler(int sig)
    {
      _sec++;
    
      if(_sec == 60)
      {
        _sec = 0;
        _min++;
    
        if(_min == 60)
        {
          _min = 0;
         _hour++;
        }
      }
    
      disp_timer();
      signal(SIGALRM, alarm_handler); /* watch on alarm again */
      alarm(1);
    }
    
    void finish(int sig)
    {
      endwin();
      exit(0);
    }
    
    int main()
    {
      int i;
      char again, ch;
    
      initscr();
      noecho();
      cbreak();
    
      timer_win = newwin(1, 10, 3, 3);
    
      disp_timer();
      signal(SIGINT, finish); /* ^C exits and cleans up program */
      signal(SIGALRM, alarm_handler);
      alarm(1);
    
      again = 1;
    
      do
      {
        for(i = 0; i < 10; i++)
        {
          clear(); /* should clear only stdscr, not timer_win */
          mvprintw(0, 0, "Question %i: ", i);
          disp_timer();
          getch();
          mvprintw(1, 0, "Answer: %i", i);
          disp_timer();
          getch();
        }
    
        clear();
        mvaddstr(0, 0, "Again (y/n)? ");
        disp_timer();
        ch = getch();
    
        if(toupper(ch) == 'N')
          again = 0;
      } while(again);
    
      finish(0);
    
      return 0;
    }

  5. #5
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    I think I'll be able to handle the cursor positioning with getyx() and move(), but the overlapping window problem still persists.

  6. #6
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    I had this wild revelation last night to use two windows, because that way the windows won't occlude one another. You don't need to use stdscr. I also found out about setitimer()
    Code:
    #include <sys/time.h>
    
    #include <ctype.h>
    #include <curses.h>
    #include <signal.h>
    #include <stdlib.h>
    #include <strings.h>
    
    int ques_x, ques_y;
    char _hour = 0, _min = 0, _sec = 0;
    WINDOW *timer_win, *ques_win;
    
    void disp_timer()
    {
      mvwprintw(timer_win, 0, 0, "%02i:%02i:%02i", _hour, _min, _sec);
      wrefresh(timer_win);
    
      /* move the cursor to where it was in ques_win */
      wmove(ques_win, ques_y, ques_x);
      wrefresh(ques_win);
    }
    
    void alarm_handler(int sig)
    {
      _sec++;
         
      if(_sec == 60)
      {
        _sec = 0;
        _min++;
      
        if(_min == 60)
        {
          _min = 0;
         _hour++;
        }   
      }
    
      disp_timer();
    }
    
    void finish(int sig)
    {
      endwin();
      exit(0);
    }
    
    int main()
    {
      int i;
      char again, ch;
      struct itimerval value;
    
      initscr();
      noecho();
      cbreak();
    
      timer_win = newwin(2, 10, 3, 0);
      ques_win = newwin(2, COLS, 0, 0);
    
      disp_timer();
      signal(SIGINT, finish); /* ^C exits and cleans up program */
      signal(SIGALRM, alarm_handler);
      bzero(&value, sizeof(value));
    
      value.it_interval.tv_sec = 1;
      value.it_value.tv_sec = 1;
    
      setitimer(ITIMER_REAL, &value, NULL); /* alarm reset after timer countdown */
    
      again = 1;
    
      do
      {
        for(i = 0; i < 10; i++)
        {
          wclear(ques_win);
          mvwprintw(ques_win, 0, 0, "Question %i: ", i);
          getyx(ques_win, ques_y, ques_x); /* save the current cursor position */
          wgetch(ques_win);
          mvwprintw(ques_win, 1, 0, "Answer: %i", i);
          getyx(ques_win, ques_y, ques_x);
          wgetch(ques_win);
        }
    
        wclear(ques_win);
        mvwaddstr(ques_win, 0, 0, "Again (y/n)? ");
        getyx(ques_win, ques_y, ques_x);      
    
        ch = wgetch(ques_win);
    
        if(toupper(ch) == 'N')
          again = 0;
      } while(again);
    
      finish(0);
    
      return 0;
    }

  7. #7
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    I also found this great tutorial:
    http://snap.nlc.dcccd.edu/learn/full...ap6/chap6.html

  8. #8
    and the hat of int overfl Salem's Avatar
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    What an ugly tutorial - wtf use is a lot of demo code if it's all rendered using images which you can't copy/paste into your own code?
    I'd search for the original tutorial that seems to be ripped from rather than that.

    As already mentioned, you have concurrency issues as well. Signal handlers are restricted environments in which only a subset of available functions are guaranteed to work properly.

  9. #9
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    I don't understand what concurrency issues I could have in the code I posted.
    I found not having the ability to copy and paste annoying, too, but the content was good. It had many examples. The professor also has many other tutorials.

  10. #10
    and the hat of int overfl Salem's Avatar
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    > I don't understand what concurrency issues I could have in the code I posted.
    Like calling mvwprintw() from within the main code and the signal handler.

  11. #11
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    Why would calling mvwprintw() within the signal handler cause concurrency issues? I have no choice: I want to be able to display the timer while accepting input from the user.

  12. #12
    and the hat of int overfl Salem's Avatar
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    > Why would calling mvwprintw() within the signal handler cause concurrency issues?
    http://www.dwheeler.com/secure-progr...O/signals.html

    > I want to be able to display the timer while accepting input from the user.
    There's always another way.

    Code:
    #include <sys/time.h>
    #include <ctype.h>
    #include <curses.h>
    #include <signal.h>
    #include <stdlib.h>
    #include <string.h> // not strings.h
    #include <errno.h>
    
    int     hour = 0, min = 0, sec = 0;
    
    void disp_timer ( WINDOW *ques_win )
    {
      mvwprintw(ques_win, 2, 0, "%02i:%02i:%02i", hour, min, sec);
      wrefresh(ques_win);
    }
    
    /* just update some simple variables in the signal handler */
    void alarm_handler ( int sig )
    {
      sec++;
      if(sec == 60)
      {
        sec = 0;
        min++;
        if(min == 60)
        {
          min = 0;
          hour++;
        }
      }
    }
    
    void finish(int sig)
    {
      endwin();
      exit(0);
    }
    
    int main()
    {
      WINDOW *ques_win;
      int     i;
      int     again, ch = 0;
      struct itimerval value;
    
      initscr();
      noecho();
      cbreak();
      halfdelay(10);
    
      ques_win = newwin(3, COLS, 0, 0);
    
      signal(SIGALRM, alarm_handler);
      memset(&value, 0, sizeof(value));
      value.it_interval.tv_sec = 1;
      value.it_value.tv_sec    = 1;
      setitimer(ITIMER_REAL, &value, NULL); /* alarm reset after timer countdown */
    
      signal(SIGINT, finish); /* ^C exits and cleans up program */
    
      again = 1;
      do
      {
        for(i = 0; i < 10;i++)
        {
          wclear(ques_win);
          disp_timer(ques_win);
          mvwprintw(ques_win, 0, 0, "Question %i: ", i);
          mvwprintw(ques_win, 1, 0, "Answer: %i", i);
          wrefresh(ques_win);
          while ( (ch = wgetch(ques_win)) == ERR ) {
            int ques_x, ques_y;
            /* timed out a second */
            /* save/restore cursor and update time */
            getyx(ques_win, ques_y, ques_x);
            disp_timer(ques_win);
            wmove(ques_win, ques_y, ques_x);
            wrefresh(ques_win);
          }
        }
    
        wclear(ques_win);
        mvwaddstr(ques_win, 0, 0, "Again (y/n)? ");
    
        ch = wgetch(ques_win);
    
        if(toupper(ch) == 'N')
          again = 0;
      } while(again);
    
      finish(0);
      return 0;
    }
    In fact, you could probably drop the timer signal altogether and just update the time at every key timeout.

  13. #13
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    The timer in your program is only updated when you press a key; it does not run at the same time as accepting input.
    Also, what's wrong with bzero()?

  14. #14
    and the hat of int overfl Salem's Avatar
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    > The timer in your program is only updated when you press a key
    Works fine here - did you remember the call to halfdelay() to cause wgetch() to return after a timeout period?

    > Also, what's wrong with bzero()?
    memset is standard, bzero isn't.

    My man page for bzero states
    This function is deprecated -- use memset in new programs.

  15. #15
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    Yes, I just copied and pasted your code. I'm on NetBSD 2.1.

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