Borys Bradel's Blog

Measuring elapsed time in programs

Tags: programming December 23, 2008    

I recently had to measure elapsed time with subsecond accuracy in C/C++ as well as Java. Since I list a number of other languages on my resume, I figure, I'd show the approach for those as well.


There are several approaches to show the elapsed time in seconds with subsecond accuracy in C/C++. The difference is in the functions that are called to measure time. The three functions clock(), gettimeofday(), and ftime() are probably the most popular ones. I will describe approaches using the first two functions.

The clock() function measures the amount of time that a process uses. The counter seems to start from 0 at the first call to clock(). The following is example code to measure elapsed (used) time using clock().

#include <time.h>

time_t start_time=clock();

... work ...

time_t end_time=clock();

double diff=(double)(end_time-start_time)/(double)CLOCKS_PER_SEC;

printf("%ld %ld %f\n",start_time,end_time,diff);

The gettimeofday() function measures the amount of time that has elapsed from a fixed point in time. The following is example code to measure elapsed time using gettimeofday().

#include <time.h>

#include <sys/time.h>

struct timeval start_time;

struct timeval end_time;


... work ...


double start_dtime=(double)start_time.tv_sec+(double)start_time.tv_usec/1000000.0;

double end_dtime=(double)end_time.tv_sec+(double)end_time.tv_usec/1000000.0; double diff=end_dtime-start_dtime;

printf("%ld %ld %f %ld %ld %f %f\n",start_time.tv_sec,start_time.tv_usec,start_dtime,end_time.tv_sec,end_time.tv_usec,end_dtime,diff);


For Java the easiest approach is to use currentTimeMillis(), which is shown in the following code.

long start_time=System.currentTimeMillis()

... work ...

long end_time=System.currentTimeMillis()

double diff=(double)(end_time-start_time)/1000.0;

System.out.println(start_time+" "+end_time+" "+diff);


For perl, the following approach works well.

#! /usr/bin/perl

use Time::HiRes; my $start_time=[Time::HiRes::gettimeofday()]; ... work ... my $diff=Time::HiRes::tv_interval($start_time); print "$diff\n";


Well, unfortunately, I know of no direct way of measuring time to subsecond accuracy with awk.

Common Lisp

For common lisp, the easiest approach is (time (progn ... work ...)). There's a reason I like common lisp.

Copyright © 2008 Borys Bradel. All rights reserved. This post is only my possibly incorrect opinion.

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