Question

When compiling a program I wrote on Mac OS X after installing the necessary libraries through MacPorts, I get this error:

In function 'nanotime':
error: 'CLOCK_REALTIME' undeclared (first use in this function)
error: (Each undeclared identifier is reported only once
error: for each function it appears in.)

It appears that clock_gettime is not implemented in Mac OS X. Is there an alternative means of getting the epoch time in nanoseconds? Unfortunately gettimeofday is in microseconds.

Answer 1

In effect, it seems not to be implemented for macOS before Sierra 10.12. You may want to look at this blog entry. The main idea is in the following code snippet:

#include <mach/mach_time.h>
#define ORWL_NANO (+1.0E-9)
#define ORWL_GIGA UINT64_C(1000000000)

static double orwl_timebase = 0.0;
static uint64_t orwl_timestart = 0;

struct timespec orwl_gettime(void) {
  // be more careful in a multithreaded environement
  if (!orwl_timestart) {
    mach_timebase_info_data_t tb = { 0 };
    mach_timebase_info(&tb);
    orwl_timebase = tb.numer;
    orwl_timebase /= tb.denom;
    orwl_timestart = mach_absolute_time();
  }
  struct timespec t;
  double diff = (mach_absolute_time() - orwl_timestart) * orwl_timebase;
  t.tv_sec = diff * ORWL_NANO;
  t.tv_nsec = diff - (t.tv_sec * ORWL_GIGA);
  return t;
}