A simple C function to time program execution down to the microsecond

demo.c

// needed for timing
#include  <stdio.h>
#include  <sys/time.h>

// needed for wasting cpu time
#include  <math.h>


long timeNow();

long timeNow(VOID)
{
  // Special struct defined by sys/time.h
  struct timeval tv;

  // Long int to store the elapsed time
  long fullTime;
  
  // This only works under GNU C I think
  gettimeofday(&tv, NULL);

  // Do some math to convert struct -> long
  fullTime = tv.tv_sec*1000000 + tv.tv_usec;
  return fullTime;
}


int main(VOID)
{
  long then, now, j;
  int i;
  
  // Initialize counter
  then = timeNow();
  
  j=0;

  // BEGIN: wasting cpu time
  for(i=1;i<1000000001;i++)
  {
    // calculate and sum a whole bunch of cube roots
    j+=pow(i,1/3.0);
  }

  // So the compiler doesn't think the loop is trivial
  j+=1;

  // END: wasting cpu time

  // grab time of completion
  now = timeNow();

  // display results :)
  printf("elapsed: %d(us)\n",now-then);

  // get more coffee
  return 0;
}

demo_results.sh

cse misc/nbenes> a.out
elapsed: 2681671(us)
cse misc/nbenes>

timer.c

#include  <stdio.h>
#include  <sys/time.h>

long timeNow(VOID)
{
  // Special struct defined by sys/time.h
  struct timeval tv;

  // Long int to store the elapsed time
  long fullTime;
  
  // This only works under GNU C I think
  gettimeofday(&tv, NULL);

  // Do some math to convert struct -> long
  fullTime = tv.tv_sec*1000000 + tv.tv_usec;
  return fullTime;
}