print_r() adds properties to DateTime objects [duplicate]

Question

Consider the following code sample:

$m_oDate = new DateTime('2013-06-12 15:54:25');
print_r($m_oDate);
echo $m_oDate->date;

Since PHP 5.3, this produces (something like) the following output:

DateTime Object
(
    [date] => 2013-06-12 15:54:25
    [timezone_type] => 3
    [timezone] => Europe/Amsterdam
)
2013-06-12 15:54:25

However the following code:

$m_oDate = new DateTime('2013-06-12 15:54:25');
echo $m_oDate->date;

...simply emits an error:

Notice: Undefined property: DateTime::$date in ...

Why does print_r() "add" these properties to the object? Note that they are not defined as part of the DateTime class on the manual page.

Answer 1

This has been reported as Bug #49382 in PHP.

In PHP 5.3, internal functionality was added to allow print_r() to show details of the underlying timestamp value held by an instance of DateTime, to assist with debugging. A side effect of this change is that when the object is dumped to text, these phantom public properties are added to the instance.

The same effect can be achieved by using reflection to access these properties, and if you need to access the properties then using reflection would be the way to go, so you don't provoke the error.

However, it should be noted that you shouldn't really use these properties - since they are not defined as members of the object, there is no guarantee they will continue to carry the same data (or even exist) in future PHP versions. If you need to access the information, use the following methods, defined as part of the API, instead:

// $obj->date
$obj->format('Y-m-d H:i:s');

// $obj->timezone
$obj->getTimezone()->getName();
// or...
$obj->getTimezone()->getOffset();
// or...
$obj->getTimezone()->listAbbreviations(); // returns an array, so may need 
                                          // further processing to be of use

NB: The timezone_type property is not accessible through the PHP API. It is an internal value and not useful in userland, because it describes the type of string that timezone holds when the object is dumped - i.e. one of the three methods for obtaining timezone information in the code sample above. For completeness, its possible values are defined in the following way:

Value | Type                  | Userland equivalent
------+-----------------------+----------------------------------
  1   | time offset           | DateTimeZone::getOffset()
  2   | TimeZone abbreviation | DateTimeZone::listAbbreviations()
  3   | TimeZone identifier   | DateTimeZone::getName()

Answer 2

There is some magic occurring but it's pretty simple.

The class DateTime doesn't have a public variable 'date' that you're meant to access. However, as a side effect of how PHP works, there is a variable created when you call print_r or var_dump on that class.

After that magic happens 'date' is available, but it shouldn't be. You should just use the getTimestamp function to make your code work reliably.