getTimestamp() : Timestamp from Date object

getTimestamp ($unixtimestamp);

date_timestamp_set ($date_obj,$unixtimestamp);

Object Oriented style

$date = new DateTime(); // current time object
echo "Timestamp: ".$date->getTimestamp()."<br>"; // getting Timestamp
echo $date->format('U = Y-m-d H:i:s');

Procedural style

$date = date_create(); // current time object
echo "Timestamp: ".date_timestamp_get($date)."<br>"; // getting Timestamp
echo date_format($date, 'U = Y-m-d H:i:s');

Timestamp of any date and time ( Object Oriented Style )

$date = new DateTime('2016-08-25 22:15:40');
echo "Timestamp: ".$date->getTimestamp();// Output is Timestamp: 1472143540

Timestamp of any date and time ( Procedural Style )

$date = date_create('2019-12-28 22:15:40');
echo "Timestamp: ".date_timestamp_get($date); // Output is Timestamp: 1577551540

Other ways to get Unix Timestamp