illustrates the problem

foo.cc (text/plain), 702 bytes, created by Denys Duchier on 2002-10-24 07:15:42 UTC

#include <iostream>
#include <unistd.h>
#include <sys/times.h>
#include <sys/time.h>
#include <unistd.h>

int main()
{
  struct tms buf;
  struct timeval begin;
  struct timeval end;
  clock_t tck_begin;
  clock_t tck_end;
  (void) gettimeofday(&begin,NULL);
  tck_begin = times(&buf);
  (void) usleep(5000000);
  tck_end = times(&buf);
  (void) gettimeofday(&end,NULL);

  std::cerr << "according to gettimeofday: "
	    << (end.tv_sec-begin.tv_sec)*1000 + (end.tv_usec-begin.tv_usec)/1000
	    << std::endl
	    << "according to ticks: "
	    << (tck_end-tck_begin)*1000/sysconf(_SC_CLK_TCK)
	    << std::endl
	    << "sysconf(_SC_CLK_TCK)=" << sysconf(_SC_CLK_TCK)
	    << std::endl;

  return 0;
}