1.2.1198. Timestamp Difference

Avoid adding or subtracting quantities of seconds to measure time.

time(), microtime() or DateTime\:\:format('U') provide timestamps, which are the number of seconds since January, 1rst, 1970. They shouldn’t be used to calculate duration or another date by adding an amount of seconds.

Those functions are subject to variations, depending on system clock variations, such as daylight saving time difference (every spring and fall, one hour variation), or leap seconds, happening on June, 30th or December 31th, as announced by IERS. When the difference may be rounded to a larger time unit (rounding the difference to days, or several hours), the variation may be ignored safely.

When the difference is very small, it requires a better way to measure time difference, such as Ticks <https://www.php.net/manual/en/control-structures.declare.php#control-structures.declare.ticks>’_, `ext/hrtime <https://www.php.net/manual/en/book.hrtime.php>’_, or including a check on the actual time zone (``ini_get()` with ‘date.timezone’).

<?php

// Calculating tomorow, same hour, the wrong way
// tomorrow is not always in 86400s, especially in countries with daylight saving
$tomorrow = time()  + 86400;

// Good way to calculate tomorrow
$datetime = new DateTime('tomorrow');

?>

See also PHP DateTime difference – it’s a trap! and PHP Daylight savings bug?.

1.2.1198.1. Suggestions

  • For small time intervals, use hrtime() functions

  • For larger time intervals, use add() method with DateTime

1.2.1198.2. Specs

Short name

Structures/TimestampDifference

Rulesets

All, Analyze, CE, CI-checks, Changed Behavior

Exakat since

0.8.4

PHP Version

All

Severity

Major

Time To Fix

Slow (1 hour)

Precision

High

Features

date

Examples

Zurmo, shopware

Available in

Entreprise Edition, Community Edition, Exakat Cloud