I need to get the number of seconds since 1970 untill the time I got after calling localtime. Is there a simple way to convert what is returning from localtime (1393340639) for example back to seconds?
Do not use localtime. Since PHP 5.2 was release, back last November 2nd 2006, you can use DateTime which offers a better interface to play with time, and which is compatible with UNIX timestamps (what you're looking for).
For example :
// always work with UTC!
date_default_timezone_set('UTC');
// support your legacy need...
$lt = localtime(1393340639);
$dt = new DateTime();
// Note : DateTime's year is 0 based, while localtime's 1900 based, so we add 1900
// Note : DateTime's month is 1 based, while localtime's 0 based, so we add 1
$dt->setDate($lt[5] + 1900, $lt[4] + 1, $lt[3]);
$dt->setTime($lt[2], $lt[1], $lt[0]);
//$dt->setTimestamp(1393340639); // <-- SAME THING!
var_dump($dt);
// output:
// object(DateTime)#1 (3) {
// ["date"]=>
// string(19) "2014-02-25 15:03:59"
// ["timezone_type"]=>
// int(3)
// ["timezone"]=>
// string(3) "UTC"
// }
echo $dt->getTimestamp();
// output: 1393340639 (which is your initial timestamp value)
You're better off not using localtime altogether, though. Just pass a DateTime object around.
If you're looking for number of seconds from 1970 till a function being called, you can use <?PHP echo time() ?>