How to subtract microtime and display date with milliseconds in php?

Question

How to subtract microtime and display date with milliseconds in php ?

For example: I have set end date and time

$endtime = 2012-02-21 10:29:59;

then I have current date or start date with converted from microtime

$starttime = 2012-02-21 10:27:59.452;

function getTimestamp()
{
        $microtime = floatval(substr((string)microtime(), 1, 8));
        $rounded = round($microtime, 3);
        return date("Y-m-d H:i:s") . substr((string)$rounded, 1, strlen($rounded));
}

echo getTimestamp(); //sample output 2012-02-21 10:27:59.452

Now I want to subtract: $finaldate = $endtime - $starttime;

I want my output to be like this: 00:00:02.452

Answer 1

You need to use microtime for the start/end values, and only format it for display at the end.

// Get the start time in microseconds, as a float value
$starttime = microtime(true);

/************/
/* Do stuff */
/************/

// Get the difference between start and end in microseconds, as a float value
$diff = microtime(true) - $starttime;

// Break the difference into seconds and microseconds
$sec = intval($diff);
$micro = $diff - $sec;

// Format the result as you want it
// $final will contain something like "00:00:02.452"
$final = strftime('%T', mktime(0, 0, $sec)) . str_replace('0.', '.', sprintf('%.3f', $micro));

Note: this is returning float values from microtime and using float arithmetic to simplify the math, so your numbers may be extremely slightly off due to the float rounding problem, but you are rounding the result to 3 digits in the end anyway, and minor fluctuations in processor timing are greater than floating point errors anyway, so this is not problem for you on multiple levels.