date format in php?

Question

PHP

$date1 = '13/12/2020';
$date2 = date("Y-m-d", strtotime($date1));
echo $date2;

This code returns '1970-01-01'. But as soon as I change $date1 = '12/12/2020' it gives '2020-12-12'. Where is the mistake?

Answer 1

The fact that in PHP there is no "date format".
There is a function strtotime that tries to guess what date you meant.
You never have to guess, you always have to know for sure.
Therefore, either change the original format, or parse it manually. date_create_from_format(), or if you're afraid of objects, then explode()

Answer 2

There are no 13 months in a year.

Answer 3

13 month does not exist =)

Answer 4

Because there is no 13th month on Earth.