[SOLVED] timer / stopwatch program in C and ncurses

metaschima · 04-07-2014, 07:55 PM

I wrote a timer program in C, but it's not too accurate. Any ideas on how to make it more accurate, like to 10 ms or 100 ms or so. It doesn't need to be too accurate, but the current one is only accurate to the nearest second or so and pausing may introduce more error.

Code:

#include <stdio.h>
#include <time.h>
#include <unistd.h>

#include <ncurses.h>

int main (int argc, char *argv[])
{
	int ch;
	unsigned int countdown;
	time_t start;
	time_t now;

	if (1 == argc)
	{
		start = time (NULL);
	}
	else if (2 == argc)
	{
		sscanf (argv[1], "%u", &countdown);
		start = time (NULL) + (countdown * 60);
	}
	else
	{
		printf ("Usage: %s <minute_countdown>\n", argv[0]);
		return 1;
	}

	initscr();
	cbreak();
	noecho();
	nodelay (stdscr, TRUE);

	int paused = 0;
	time_t prev = 0;
	for (;;)
	{
		if (0 == paused)
		{
			now = time (NULL) - start;
			if (now != prev)
			{
				mvprintw (1, 2, "%+04d:%+03d", now / 60 , now % 60);
				refresh();
				prev = now;
			}
		}
		else
		{
			start = time (NULL) - now;
		}

		if (ERR != (ch = getch()))
		{
			if (27 == ch)
			{
				break;
			}
			else
			{
				if (0 == paused)
				{
					attron (A_STANDOUT);
					paused = 1;
				}
				else
				{
					attroff (A_STANDOUT);
					paused = 0;
				}
				mvprintw (1, 2, "%+04d:%+03d", now / 60 , now % 60);
				refresh();
			}
		}
		usleep(100000);
	}

	endwin();
	return 0;
}

It works well, and I'll keep using it, but I'm sure there's another way. I still need to be able to pause it and resume it, as that's the most important feature, and countdown.

Oh, and it should stay mostly portable, but I only run Linux.

I was thinking of using usleep to pause for certain time, but I feel that the commands in-between will gradually add time to it and make it inaccurate, so before doing that I'm asking for other methods.

Thanks

gengisdave · 04-07-2014, 10:28 PM

use gettimeofday, it uses a struct to store sec/msec

metaschima · 04-08-2014, 03:37 PM

I decided to use clock_gettime as it is recommended over gettimeofday, but it still doesn't work quite right, I'll have to think this over a bit. Maybe the math is wrong.

Code:

#include <stdio.h>
#include <time.h>
#include <unistd.h>

#include <ncurses.h>

int main (int argc, char *argv[])
{
	int ch;
	unsigned int countdown;
	struct timespec start;
	struct timespec now;

	clock_gettime(CLOCK_MONOTONIC, &start);
	if (2 == argc)
	{
		sscanf (argv[1], "%u", &countdown);
		start.tv_sec += countdown * 60;
	}
	else if (1 != argc)
	{
		printf ("Usage: %s <minute_countdown>\n", argv[0]);
		return 1;
	}

	initscr();
	cbreak();
	noecho();
	nodelay (stdscr, TRUE);

	int paused = 0;
	struct timespec prev = start;
	for (;;)
	{
		if (0 == paused)
		{
			clock_gettime(CLOCK_MONOTONIC, &now);
			now.tv_sec -= start.tv_sec;
			now.tv_nsec -= start.tv_nsec;
			if (now.tv_sec != prev.tv_sec && now.tv_nsec != prev.tv_nsec)
			{
				mvprintw (1, 2, "%+04d:%+03d:%+03d", now.tv_sec / 60 , now.tv_sec, now.tv_nsec/1000000);
				refresh();
				prev = now;
			}
		}
		else
		{
			clock_gettime(CLOCK_MONOTONIC, &start);
			start.tv_sec -= now.tv_sec;
			start.tv_nsec -= now.tv_nsec;
		}

		if (ERR != (ch = getch()))
		{
			if (27 == ch)
			{
				break;
			}
			else
			{
				if (0 == paused)
				{
					attron (A_STANDOUT);
					paused = 1;
				}
				else
				{
					attroff (A_STANDOUT);
					paused = 0;
				}
				mvprintw (1, 2, "%+04d:%+03d:%+03d", now.tv_sec / 60 , now.tv_sec, now.tv_nsec/1000000);
				refresh();
			}
		}
		usleep(100000);
	}

	endwin();
	return 0;
}

metaschima · 04-08-2014, 08:14 PM

Alright, I think I got it, here's the final version.

Code:

#include <stdio.h>
#include <time.h>

#include <ncurses.h>

inline void subtract_time (struct timespec * __restrict later, struct timespec * __restrict former)
{
	clock_gettime(CLOCK_MONOTONIC, later);
	later->tv_sec -= former->tv_sec;
	if (later->tv_nsec < former->tv_nsec)
	{
		later->tv_sec--;
		later->tv_nsec = 1000000000 + later->tv_nsec - former->tv_nsec;
	}
	else
	{
		later->tv_nsec -= former->tv_nsec;
	}
}

int main (int argc, char *argv[])
{
	int ch;
	unsigned int countdown;
	struct timespec start;
	struct timespec now;

	clock_gettime(CLOCK_MONOTONIC, &start);
	if (2 == argc)
	{
		sscanf (argv[1], "%u", &countdown);
		start.tv_sec += countdown * 60;
	}
	else if (1 != argc)
	{
		printf ("Usage: %s <minute_countdown>\n", argv[0]);
		return 1;
	}

	initscr();
	cbreak();
	noecho();
	nodelay (stdscr, TRUE);

	struct timespec delay;
	delay.tv_sec = 0;
	delay.tv_nsec = 1000000;

	int paused = 0;
	struct timespec prev = start;
	for (;;)
	{
		if (0 == paused)
		{
			subtract_time (&now, &start);
			if (now.tv_sec != prev.tv_sec)
			{
				mvprintw (1, 2, "%+04d:%+03d", now.tv_sec / 60 , now.tv_sec % 60);
				refresh();
				prev = now;
			}
		}
		else
		{
			subtract_time (&start, &now);
		}

		if (ERR != (ch = getch()))
		{
			if (27 == ch)
			{
				break;
			}
			else
			{
				if (0 == paused)
				{
					attron (A_STANDOUT);
					paused = 1;
				}
				else
				{
					attroff (A_STANDOUT);
					paused = 0;
				}
				mvprintw (1, 2, "%+04d:%+03d", now.tv_sec / 60 , now.tv_sec % 60);
				refresh();
			}
		}
		clock_nanosleep (CLOCK_MONOTONIC, 0, &delay, NULL);
	}

	endwin();
	return 0;
}

It works well, so I will mark this solved. If someone sees an error, tell me.