Printing Time since Epoch in Nanoseconds

问题

So I know how to print time since epoch in seconds, and evidently even milliseconds, but when I try nanoseconds I keep getting bogus output of an integer that's way too small, and it sometimes prints numbers smaller than the last run.

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

int main (void)
{
    long int ns;
    struct timespec spec;

    clock_gettime(CLOCK_REALTIME, &spec);
    ns = spec.tv_nsec;;

    printf("Current time: %ld nonoseconds since the Epoch\n", ns);
    return 0;
}

For instance, with a run from this I got 35071471 nanoseconds since epoch.

Any help with getting this to display correctly would be appreciated.

回答1:

The nanosecond part is just the "fractional" part, you have to add the seconds, too.

// otherwise gcc with option -std=c11 complaints
#define _POSIX_C_SOURCE 199309L
#include <stdio.h>
#include <time.h>
#include <stdint.h>
#include <inttypes.h>
#define BILLION  1000000000L
int main(void)
{
  long int ns;
  uint64_t all;
  time_t sec;
  struct timespec spec;

  clock_gettime(CLOCK_REALTIME, &spec);
  sec = spec.tv_sec;
  ns = spec.tv_nsec;

  all = (uint64_t) sec * BILLION + (uint64_t) ns;

  printf("Current time: %" PRIu64  " nanoseconds since the Epoch\n", all);
  return 0;
}

来源：https://stackoverflow.com/questions/39439268/printing-time-since-epoch-in-nanoseconds