How does PHP compare DateTime
objects when using conditional operators (<
, >
, >=
, <=
) ?
Is this comparison timezone invariant?
I tried below code and It looks like it is timezone invariant, can anyone confirm?
Code:
$datestr = "2015-10-09 10:28:01";
$dt = new DateTime($datestr);
$nowdate = new DateTime("now",new DateTimeZone("CET"));
print_r($dt);
echo "<br/>";
print_r($nowdate);
echo "<br/>";
var_dump($nowdate<$dt);
Output:
DateTime Object ( [date] => 2015-10-09 10:28:01 [timezone_type] => 3 [timezone] => Europe/Paris )
DateTime Object ( [date] => 2015-10-09 10:53:42 [timezone_type] => 2 [timezone] => CET )
boolean false
According to the manual:
As of PHP 5.2.2, DateTime objects can be compared using comparison operators.
You've chosen a very confusing example that includes a fixed date that's not clear if it's supposed to be in the past and a time zone that's currently not active (it's CEST here in Western Europe until the end of October). Whatever, I see nothing wrong in your output: 2015-10-09 10:53:42 CET
(which equals 2015-10-09 09:53:42 UTC
) is clearly greater than 2015-10-09 10:28:01 Europe/Paris
(which equals 2015-10-09 08:28:01 UTC
).
With a slightly better example we can guess the operands do work as expected:
echo "Same date:\n";
$a = new DateTime('2015-01-31 01:23:45 UTC');
$b = new DateTime('2015-01-31 02:23:45 Europe/Paris');
var_dump($a, $b, $a<$b, $a==$b, $a>$b);
echo "\n";
echo "First greater than second:\n";
$a = new DateTime('2015-01-31 01:23:46 UTC');
$b = new DateTime('2015-01-31 02:23:45 Europe/Paris');
var_dump($a, $b, $a<$b, $a==$b, $a>$b);
echo "\n";
echo "First less than second:\n";
$a = new DateTime('2015-01-31 01:23:45 UTC');
$b = new DateTime('2015-01-31 02:23:46 Europe/Paris');
var_dump($a, $b, $a<$b, $a==$b, $a>$b);
Same date:
[...]
bool(false)
bool(true)
bool(false)
First greater than second:
[...]
bool(false)
bool(false)
bool(true)
First less than second:
[...]
bool(true)
bool(false)
bool(false)
Demo with full code.
Another example:
$date_2014 = new DateTime('2014-12-31 23:00:00 -07:00');
$date_2015 = new DateTime('2015-01-01 05:00:00 Asia/Tokyo');
var_dump($date_2014<$date_2015); // bool(false)
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