How to use timer in C?

How to use timer in C?

Heres a solution I used (it needs #include <time.h>):

int msec = 0, trigger = 10; /* 10ms */
clock_t before = clock();

do {
  /*
   * Do something to busy the CPU just here while you drink a coffee
   * Be sure this code will not take more than `trigger` ms
   */

  clock_t difference = clock() - before;
  msec = difference * 1000 / CLOCKS_PER_SEC;
  iterations++;
} while ( msec < trigger );

printf(Time taken %d seconds %d milliseconds (%d iterations)n,
  msec/1000, msec%1000, iterations);

You can use a time_t struct and clock() function from time.h.

Store the start time in a time_t struct by using clock() and check the elapsed time by comparing the difference between stored time and current time.

How to use timer in C?

Yes, you need a loop. If you already have a main loop (most GUI event-driven stuff does) you can probably stick your timer into that. Use:

#include <time.h> 
time_t my_t, fire_t;

Then (for times over 1 second), initialize your timer by reading the current time:

my_t = time(NULL);

Add the number of seconds your timer should wait and store it in fire_t. A time_t is essentially a uint32_t, you may need to cast it.

Inside your loop do another

my_t = time(NULL);

if (my_t > fire_t) then consider the timer fired and do the stuff you want there. That will probably include resetting it by doing another fire_t = time(NULL) + seconds_to_wait for next time.

A time_t is a somewhat antiquated unix method of storing time as the number of seconds since midnight 1/1/1970 but it has many advantages. For times less than 1 second you need to use gettimeofday() (microseconds) or clock_gettime() (nanoseconds) and deal with a struct timeval or struct timespec which is a time_t and the microseconds or nanoseconds since that 1 second mark. Making a timer works the same way except when you add your time to wait you need to remember to manually do the carry (into the time_t) if the resulting microseconds or nanoseconds value goes over 1 second. Yes, its messy. See man 2 time, man gettimeofday, man clock_gettime.

sleep(), usleep(), nanosleep() have a hidden benefit. You see it as pausing your program, but what they really do is release the CPU for that amount of time. Repeatedly polling by reading the time and comparing to the done time (are we there yet?) will burn a lot of CPU cycles which may slow down other programs running on the same machine (and use more electricity/battery). Its better to sleep() most of the time then start checking the time.

If youre trying to sleep and do work at the same time you need threads.