Timers in c

I wanted to know if theres any timers in C linux programming and if anyone could give an example. So I don't want something like sleep(). Because I want the timer in an if statement since the statement will be in an infinite while loop. That onces the timer goes off then the program will process the code in the if statement. Is there anything like that in C linux.

So look in <time.h> for the standard stuff, and maybe unistd.h if you want something Linux specific, for getting the current time. (Presumably you'd get the time when you start the clock and then use something like difftime to get the current reading of the clock.)

So I looked it up and It doesnt really seem to get any data types towards teh milisecond acting as a stop watch kind of. Is the only method have two timers and getting the differences until it matches up with the desired time?

Code:

---

man gettimeofday
man ftime

---

Quote:

---

Originally Posted by kiros88

So I looked it up and It doesnt really seem to get any data types towards teh milisecond acting as a stop watch kind of. Is the only method have two timers and getting the differences until it matches up with the desired time?

---

Are you thinking of something like sleep(in seconds), or delay(in milliseconds) ?

You can use the alarm() or ualarm() function to trigger an event after the specified number of seconds / microseconds have elapsed. Trap the SIGALRM signal by writing a signal handler and put the if-else statement inside it.

. . . then there is always nanosleep()

Quote:

---

Originally Posted by kiros88

Is the only method have two timers and getting the differences until it matches up with the desired time?

---

That is why they call it "low level programming" :p

Since you are using linux, you can use Glib. Take a look here:

Timers

(Ignore the fact that this is presented as part of the GNOME documentation, it does not require or depend on GNOME)

Then take a look here

The Main Event Loop

and search for "g_timeout_add". This allows you to set a callback to occur at a certain time, IF you are using the Glib "main event loop".

Which is a lot to swallow all at once, but Glib has TONS of functionality build into it -- complex datatypes like linked lists and hash tables, "g" threads, IO channels, on and on, it's a kind of whahoo! shopping spree library and if you intend to program for linux worth the time.

I don't want to sleep or delay the program because i want the rest of the code to be runnning since im planning to just use the timer for and if else statement. I was looking for alarm() but what header file uses it

So you want it like a stopwatch?

Why not just save the start time and trigger when the difference is right?

If you want to know how alarm() works, type the command "man alarm".

alarm() is limited to an integer number of seconds for the delay. These days it is more common to use setitimer() instead which allows for sub-second delays.

Does anyone have a really simple example of setitimer I'm looking online and I found one but its kinda of confusing to understand

Code:

---

#include <stdio.h>
#include <signal.h>
#include <sys/time.h>

#define INTERVAL 5

int howmany = 0;
void alarm_wakeup (int i)
{
  struct itimerval tout_val;
  signal(SIGALRM,alarm_wakeup);
  howmany += INTERVAL;
  printf("\n%d sec up partner, Wakeup!!!\n",howmany);
  tout_val.it_interval.tv_sec = 0;
  tout_val.it_interval.tv_usec = 0;
  tout_val.it_value.tv_sec = INTERVAL; /* 10 seconds timer */
  tout_val.it_value.tv_usec = 0;
  setitimer(ITIMER_REAL, &tout_val,0);
}

void exit_func (int i)
{
    signal(SIGINT,exit_func);
    printf("\nBye Bye!!!\n");
    exit(0);
}

int main ()
{
  struct itimerval tout_val;
 
  tout_val.it_interval.tv_sec = 0;
  tout_val.it_interval.tv_usec = 0;
  tout_val.it_value.tv_sec = INTERVAL; /* 10 seconds timer */
  tout_val.it_value.tv_usec = 0;
  setitimer(ITIMER_REAL, &tout_val,0);

  signal(SIGALRM,alarm_wakeup); /* set the Alarm signal capture */
  signal(SIGINT,exit_func);
 
  while (1)
  {
    //printf("!");
  }
  return 0;
}

---

I dont really understand what calls the exit signal

Perhaps start off with the simpler alarm() interface before moving to setitimer(). If you want to set a timer in milliseconds then consider using the microseconds analog of alarm() ie ualarm().