Delan Azabani Delan Azabani - 1 year ago 241
C Question

clock_gettime alternative in Mac OS X

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

Answer Source

In effect, it seems not to be implemented for MacOs. You may want to look at this blog entry, but this doesn't seem to be available anymore. 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 };
    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;
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