#ifdef _WIN32
        #include <windows.h>
#elif MACOS
        #include <sys/param.h>
        #include <sys/sysctl.h>
#else
        #include <unistd.h>
#endif

int getNumberOfCores() {

#ifdef WIN32
    SYSTEM_INFO sysinfo;
    GetSystemInfo(&sysinfo);
    return sysinfo.dwNumberOfProcessors;

#elif MACOS
    int nm[2];
    size_t len = 4;
    uint32_t count;

    nm[0] = CTL_HW; nm[1] = HW_AVAILCPU;
    sysctl(nm, 2, &count, &len, NULL, 0);

    if(count < 1) {
    nm[1] = HW_NCPU;
    sysctl(nm, 2, &count, &len, NULL, 0);
    if(count < 1) { count = 1; }
    }
    return count;
#else

    return sysconf(_SC_NPROCESSORS_ONLN);
#endif

}

# example
# printf("%x", getNumberOfCores());