// test sleep() and msec() timing
//
#include <stdio.h>
#include <unistd.h>   // unsigned int sleep(unsigned int seconds)
#include <sys/time.h> // int gettimeofday(struct timeval *tv, struct timezone *tz)

double msec( void) // time in milliseconds
{
  struct timeval tv;

  if( gettimeofday(&tv,0) < 0) { perror("gettimeofday"); return 0; }

  return tv.tv_sec*1000.0 + tv.tv_usec/1000.0;
}

int main( void)
{
  printf( "sleeping for 1 second...\n");

  double t0 = msec();

  sleep(1);

  double t1 = msec();

  printf( "elapsed time %g msec\n", t1-t0);

  return 0;
} 

/* sample output:

sleeping for 1 second...
elapsed time 1000.33 msec

*/