clock_gettime on MacOS

Question

clock_gettime doesn't work on MacOS Sierra anymore. Pretty sure I had this compiling correctly before Xcode 8 came out. I am really kind of stuck on what to do to get it to compile correctly.

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#include <time.h>

int main(){
    struct timespec time1, time2;

    clock_gettime(CLOCK_MONOTONIC,&time1);
    //Some code I am trying to work out performance of...
    clock_gettime(CLOCK_MONOTONIC,&time2);
    printf("Time Taken: %ld",time2.tv_nsec - time1.tv_nsec);
}

Code like this simply fails to compile. I've been told the sierra timing library has changed. I get a compiler error for CLOCK_MONOTONIC not being defined and a warning for implicit declaration of clock_gettime, which turns into an error if I define CLOCK_MONOTONIC to something random, as it then just errors out during the linking stage.

Does anyone know of a fix or workaround to get the code compiling and executing?

score 2 · Accepted Answer · edited May 23 '17 at 12:01

I don't think CLOCK_MONOTONIC has been around in recent times.

I believe what you want is probably mach_absolute_time() plus a conversion, as documented here; this appears to be monotonic, and absolute (which are two different things as you probably know).

Other useful hints are to be found at the following related (but I think not duplicate) questions:

clock_gettime alternative in Mac OS X (but deals with a different clock type)
Monotonic clock on OSX (not C but objective C)

clock_gettime on MacOS

1 Answers1