Creating a simple timer application - c

Question

gcc 4.4.3
vc++ 2008
I would like to make a timer application would be portable on windows and linux. However, would be suffice to start with.
My idea is to start a timer and set it for a specified number of seconds. When the time expires call a callback function.
Is that the best way to do this?
Many thanks,

Answer 1

There are many ways to do a timer. It is not hard but you need to think exactly what you want. If you want to call a callback, you usually use a thread that sleep until your delay is elapsed, before calling your callback. If you don't want to use a thread, you can call periodically a checker function that compute the time delta.
You api will be a function taking the delay and a function pointer plus the callback parameters. It will launch a thread that will sleep for the delay, then call the callback with the given parameters.
Check general purpose libraries, they usually have timers implemented (gtk+ glib, boost::timer I think).
my2c
Edit:
For the portability part, you have of course to write two versions of your timer function. If you use thread that means it is better to use a lib. As libs give you timers ... Use a lib :)

Answer 2

Windows and linux do timers differently. I suggest that you encapsulate the timing functionality into a class. You'll have to write the class twice (once for each platform) but then the rest of the program can be the same.
Alternatively you can use a toolkit where somebody else gas already done it for you. e.g. QT or Boost.

Answer 3

I have worked with several such timers in both C and C++. For C GTK example on the following url may be helpful http://zetcode.com/tutorials/gtktutorial/gtkevents/. In C++ I used glib timer https://developer.gnome.org/glibmm/2.34/classGlib_1_1SignalTimeout.html (although it is not precise). I also work with libev (which uses epoll() on Linux and select() on Windows) for better precision timer. For C, I present an example below
//This program is demo for using pthreads with libev.
//Try using Timeout values as large as 1.0 and as small as 0.000001
//and notice the difference in the output
//(c) 2013 enthusiasticgeek for stack overflow
//Free to distribute and improve the code. Leave credits intact
//On Ubuntu (assuming libev is installed) compile with the command - gcc -g test.c -o test -lev
#include <ev.h>
#include <stdio.h> // for printf
#include <stdlib.h>
double timeout = 1.0; //seconds
ev_timer timeout_watcher;
int timeout_count = 0;
static void timeout_cb (EV_P_ ev_timer *w, int revents) // Timer callback function
{
++timeout_count;
printf("%d\n", timeout_count);
w->repeat = timeout;
ev_timer_again(loop, &timeout_watcher); //Start the timer again.
}
int main (int argc, char** argv)
{
struct ev_loop *loop = EV_DEFAULT; //or ev_default_loop (0);
ev_timer_init (&timeout_watcher, timeout_cb, timeout, 0.); // Non repeating timer. The timer starts repeating in the timeout callback function
ev_timer_start (loop, &timeout_watcher);
// now wait for events to arrive
ev_loop(loop, 0);
return 0;
}
For more docs on libev view http://doc.dvgu.ru/devel/ev.html