php DateTime createFromFormat functionality

Question

Hi I seem to be having trouble getting the datetime method to work as expected? I may be doing something wrong?

// Passes OK 
$dateTime = DateTime::createFromFormat('d/m/Y', '12/12/2012' );
var_dump($dateTime);

// should fail but returns  - 2016-09-25 
$dateTime = DateTime::createFromFormat('d/m/Y', '56/56/2012' );
var_dump($dateTime);

// correctly returns False 
$dateTime = DateTime::createFromFormat('d/m/Y', '56/56/fail' );
var_dump($dateTime);

// should fail but returns 2019-08-29 09:58:10
$dateTime = DateTime::createFromFormat('m/d/Y', '90/90/2012' );
var_dump($dateTime);

Answer 1

The thing about DateTime::createFromFormat is that there are two kinds of unexpected input it recognizes: the kind that generates errors, and the kind that generates warnings.

Input such as '56/56/fail' produces an error, so false is returned and everything is good. However, '56/56/2012' gives not an error but a warning, and is actually parsed as the 56th day of the 56th month of 2012. Since 2012 does not have 56 months, PHP internally changes this to 2016 + 8 months = Aug 2016. And since that month does not have 56 days, we have another compensation to Sep 2016 + (56 - 31) days = 25 Sep 2016. So while unexpected, this is in fact correct.

If you want to disallow this automatic adjustment, you have to wrap the DateTime factory method and use DateTime::getLastErrors as reference:

$dateTime = DateTime::createFromFormat('d/m/Y', '56/56/2012');
$errors = DateTime::getLastErrors();
if (!empty($errors['warning_count'])) {
    echo "Strictly speaking, that date was invalid!\n";
}

See it in action.

Answer 2

PHP is a strange beast (to say the least). 56/56/2012 results in all additional months and days to be added to the date until it becomes correct (god only knows the logic behind this).