DateTime instance property changes due to a var_dump() or print_r()

Question

I have the following code:

<?php

$date = new DateTime;
var_dump($date);
$date->timezone = 'Europe/Madrid';
var_dump($date->timezone);  // Shows 'Europe/Madrid'
var_dump($date);            // Shows 'UTC' (!)
var_dump($date->timezone);  // Shows 'UTC' (!!)

which shows the following output:

object(DateTime)#1 (3) {
  ["date"]=>
  string(26) "2017-11-08 21:21:15.596968"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(3) "UTC"
}
string(13) "Europe/Madrid"
object(DateTime)#1 (3) {
  ["date"]=>
  string(26) "2017-11-08 21:21:15.596968"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(3) "UTC"
}
string(3) "UTC"

Why $date->timezone changes back from 'Europe/Madrid' to 'UTC' when I do a simple var_dump($date)???

Using print_r() instead of var_dump() has the same result.

Answer 1

timezone is not a property of a new DateTime class. You can verify that by trying to access it immediately after creating the DateTime object.

$date = new DateTime;
echo $date->timezone;

This will get you an undefined property notice.

PHP creates the timezone property to display when you do print_r or var_dump on the object, but modifying that property does not modify the underlying data.

The next time you var_dump or print_r the object, the display properties will be regenerated, overwriting your changes.

You can use the setTimezone method instead if you really do need to change the timezone.

$date->setTimezone(new DateTimeZone('Europe/Madrid'));

(Or set the timezone in your PHP configuration.)

---

Interestingly enough, referring directly to the timezone property still shows the old value even after you update it with setTimezone. Apparently you need to var_dump the whole object for it to recreate those properties.

$date = new DateTime;
var_dump($date);     // Shows 'UTC'
$date->setTimezone(new DateTimeZone('Europe/Madrid'));
var_dump($date->timezone);  // Still shows 'UTC' (!)
var_dump($date);            // Shows 'Europe/Madrid'
var_dump($date->timezone);  // Shows 'Europe/Madrid'