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

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;
}

---

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]

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;
}

---

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

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;
}

---

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

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.

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.

> 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.

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.

> 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.

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()?

> 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.

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

Puzzled.
I'm using Fedora FC4, and the ncurses library is version 5.4

Here's what I've found:
- your program works fine on Debian when using curses
- your program works fine when using the ncurses library on NetBSD, but the getyx() macro does not seem to be defined properly. I get the following errors:
/var/tmp//cckfwyCa.o(.text+0x1ca): In function `main':
: undefined reference to `getcury'
/var/tmp//cckfwyCa.o(.text+0x1db): In function `main':
: undefined reference to `getcurx'
Note that the ncurses library does not come installed with NetBSD; you have to install it as a package
- my version of the program works fine on Debian.

However, Debian is not my development environment. I do all of my development on NetBSD; the NetBSD box I have is not networked, so I can't SSH into the Debian box.

[edit]When I compiled the program on NetBSD, I wasn't including ncurses.h. When I did so, the program worked fine. Doing a diff on ncurses.h and curses.h in Debian reveals that the files are the same. ncurses seems to have the exact same interface as curses.[/edit]

The interface may be the same, but internal functionality is obviously different. Compiling your program with curses.h and linking to curses on NetBSD does not produce an updating timer as it does using ncurses.