为什么本地时间戳等于UTC时间戳？ [重复]

Question

This question already has an answer here:

• UNIX timestamp always in GMT? 5 answers

If date() formats a local time/date, and gmdate() formats a GMT/UTC date/time, why is this true?

date_default_timezone_set('America/Los_Angeles');
var_dump(date('U') === gmdate('U')); // true

On the command line:

$ php -r "date_default_timezone_set('America/Los_Angeles'); var_dump(date('U') === gmdate('U'));"
bool(true)

Why is the local timestamp equal to the UTC timestamp for different time zones?

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Answer 1

Because timestamps are seconds since the Unix Epoch (January 1 1970 00:00:00 GMT). Notice the GMT? No matter what time zone you're in, the timestamp is relative to that time and timezone.

What you really want to do is:

$local = new DateTime();
$local->setTimeZone(new DateTimeZone('America/Los_Angeles'));
$gmt   = new DateTime();
$gmt->setTimeZone(new DateTimeZone('UTC'));
var_dump($local === $gmt);