- print_r: documentation ( source)
- explode: documentation ( source)
<?php
$date_str = '2013-12-12 12:45:45';
$date = DateTime::createFromFormat( 'Y-m-d|', explode( ' ', $date_str)[0] )->format('U');
print_r($date);
//print_r($date->format('U'));
//$ts = DateTime::createFromFormat( 'U', $date_str->format('Y-m-d') );
//print_r( $ts->format('U'));