dateTime.php

<?php
// --- DateTime construct

$date = new DateTime('2015-02-31');             // max. 28 of Feb
echo $date->format('Y-m-d') . PHP_EOL;          // 2015-03-03

// Fatal error: Uncaught exception 'Exception' with message
// 'DateTime::__construct(): Failed to parse time string (2015-02-32) at position 9 (2): Unexpected character'
//$date = new DateTime('2015-02-32');

//--- DateTime sub
$date = new DateTime('2015-05-31');
$date->sub(new DateInterval('P1M'));

// 2015-05-01, because it was internally changed to 2015-04-31, which doesn't exist
// so was again changed to the next day
echo $date->format('Y-m-d') . PHP_EOL;

$date->setDate(2014, 14, 32);   // 2015-03-04 no fatal error, setDate() calculates days
echo $date->format('Y-m-d') . PHP_EOL;


//--- DateTime createFromFormat
$format = 'Y-m-!d H:i:s';
$date = DateTime::createFromFormat($format, '2009-02-15 15:16:17');
echo $date->format('Y-m-d H:i:s') . "\n"; // 1970-01-15 15:16:17