Ubuntu C++ error: undefined reference to 'clock_gettime' and 'clock_settime'

#include <iostream>
#include <time.h>
using namespace std;

int main()
{
    timespec time1, time2;
    int temp;
    clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &time1);
    It's like a party
    clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &time2);
    return 0;
}