PHP: DateTime '-1 day'

Question

I want to get the date of yesterday of the current date in a specifc time zone. I tried like this, but it is not working:

$date = new DateTime(NULL, new DateTimeZone('Pacific/Wake')); 
$yesterday = $date->modify( '-1 day' );
$yesterday = $yesterday->format('Y-m-d');

I am still getting today's date.

Answer 1

This problem, according to the documentation for the modify() method, seems to entirely depend on which version of php you're using. In this case, method chaining(which is what you're attempting to do is called), is only available on php version 5.3.0 and up, according to the changelog on the previously linked docs.

That in mind, it explains why your code didn't work, and @Deryck's did. If you ever do upgrade your php version, or get your host to upgrade it, you could likely reduce those three lines to two:

$date = new DateTime(NULL, new DateTimeZone('Pacific/Wake')); 
$date = $date->modify( '-1 day' )->format('Y-m-d');

Not much of an improvement, I realize, but there's your reason for why it failed to work.

Below are two of the methods I see of getting around this; one is creation of a class.. which seems like overkill to me unless this is apart of something grander... the other is a creation of a function. Both shove the extra lines into something that takes up less space, in a sense.

class DT {
    private $now; //can be null
    private $timezone; //DateTimeZone object
    public function __construct($tz_str, $now = NULL) {
        $this->now = $now;
        $this->timezone = new DateTimeZone($tz_str);;
    }

    public function mod($mod,$format) {
      $dt = new DateTime($this->now, $this->timezone);
      $dt->modify($mod);
      return $dt->format($format);
    }
}

function mod_formatted_zone($tz_str, $mod, $format, $now = NULL) {
    $timezone = new DateTimeZone($tz_str);
    $dt = new DateTime($now,$timezone);
    $dt->modify($mod);
    return $dt->format($format);
}

The use of either is simple; in the case of the class, it'd be something like..

$dt = new DT('Pacific/Wake');
echo $dt->mod('-1 day', 'Y-m-d');

While in the case of the function, it'd simply be..

echo mod_formatted_zone('Pacific/Wake', '-1 day', 'Y-m-d');