How do I get the earliest possible datetime in php?

Question

My understanding is that datetimes in php are represented as the number of milliseconds after a certain date (some time in 1960 I think?). How to I construct a datetime that represents the earliest allowable date in php? An example possible syntax would be:

$date = new DateTime(0);

but this doesn't work. Is there some other way to do this?

Thanks for any input.

Answer 1

echo date('d-m-Y', 0); // outputs: 01-01-1970

epoch 0 gives the unix timestamp 01-01-1970 or 00:00:00 UTC on January 1st 1970.

Answer 2

You're pretty close

$date = (new DateTime())->setTimestamp(0);

Will give January 1st, 1970

Answer 3

I think the smallest and largest dates that the DateTime object will accept are as follows (on a 64 bit machine as of PHP 7.4, demonstrated using PHPUnit). This can be useful in providing default mins and maxes on a date validator for both DateTime as well as Carbon. This answer is also posted in the user contributed notes of the PHP manual page for DateTime::__construct().

If you want to get very precise about it, modify the code below to account for time and timezone.

    // smallest date
    $input = '-9999-01-01';
    $dt = new \DateTime($input);
    self::assertEquals($input, $dt->format('Y-m-d'));
    $input = '-10000-12-31';
    $dt = new \DateTime($input);
    self::assertEquals('2000-12-31', $dt->format('Y-m-d'));

    // largest date
    $input = '9999-12-31';
    $dt = new \DateTime($input);
    self::assertEquals($input, $dt->format('Y-m-d'));
    $input = '10000-01-01';
    $dt = new \DateTime($input);
    self::assertEquals('2000-01-01', $dt->format('Y-m-d'));