How to get the current time in milliseconds from C in Linux?

Question

How do I get the current time on Linux in milliseconds?

Answer 1

This can be achieved using the POSIX clock_gettime function.

In the current version of POSIX, gettimeofday is marked obsolete. This means it may be removed from a future version of the specification. Application writers are encouraged to use the clock_gettime function instead of gettimeofday.

Here is an example of how to use clock_gettime:

#define _POSIX_C_SOURCE 200809L  #include <inttypes.h> #include <math.h> #include <stdio.h> #include <time.h>  void print_current_time_with_ms (void) {     long            ms; // Milliseconds     time_t          s;  // Seconds     struct timespec spec;      clock_gettime(CLOCK_REALTIME, &spec);      s  = spec.tv_sec;     ms = round(spec.tv_nsec / 1.0e6); // Convert nanoseconds to milliseconds     if (ms > 999) {         s++;         ms = 0;     }      printf("Current time: %"PRIdMAX".%03ld seconds since the Epoch\n",            (intmax_t)s, ms); } 

If your goal is to measure elapsed time, and your system supports the "monotonic clock" option, then you should consider using CLOCK_MONOTONIC instead of CLOCK_REALTIME.