PHP日期中的奇怪行为

Question

A simple code to print a date

$first_date = 1319493600;
$last_date = 1320184800;

$testDate = $first_date;


while ($testDate<=$last_date)
{
    echo strftime("%a", $testDate).' '. strftime("%d", $testDate).' '.strftime("%b", $testDate).'<br>';
    $testDate += 86400;
}

Yes this simple script fails me as you see below

Tue 25 Oct
Wed 26 Oct
Thu 27 Oct
Fri 28 Oct
Sat 29 Oct
Sun 30 Oct <----Error
Sun 30 Oct <----Error
Mon 31 Oct
Tue 01 Nov

Anyone has any idea why?

Answer 1

Looks like it's related to DST .. clocks are changed on the last sunday of october, in this year Sun 30 Oct.

Note: you also have to be in the "right" timezone for this to happen, eg here it's:

 # date -ud@1319493600
 Mon Oct 24 22:00:00 UTC 2011

so that one hour doesn't make any difference, but for you it does. This can be quite annoying as people won't be able to reproduce your problem :)

Answer 2

This is, in fact, the reason why you should never increment the day by adding 24 hours to the timestamp. Chances are that you are in a timezone that observes daylight saving time and the last Sunday of October is not 24 hours long.

You can confirm this by adding echo strftime("%r %x", $testDate); inside the loop. (Also note that you can use multiple modifiers in strftime() so you don't have to concatenate them: strftime("%a %d %b", $testDate); .)

Always use date functions like strtotime() or mktime() to increment the date.

Answer 3

This probably has to do with the daylight savings time change on 30 Oct. Try running the script with the times printed out too to see the change. Here's an example in my timezone:

php > $first_date = 1319493600;
php > $last_date = 1320184800;
php >
php > $testDate = $first_date;
php >
php >
php > while ($testDate<=$last_date)
php > {
php {     echo strftime("%a", $testDate).' '. strftime("%d", $testDate).' '.strftime("%b", $testDate). '(' . strftime("%d.%m.%Y %H:%M:%S", $testDate) . ")\n";
php {     $testDate += 86400;
php { }
Mon 24 Oct(24.10.2011 23:00:00)
Tue 25 Oct(25.10.2011 23:00:00)
Wed 26 Oct(26.10.2011 23:00:00)
Thu 27 Oct(27.10.2011 23:00:00)
Fri 28 Oct(28.10.2011 23:00:00)
Sat 29 Oct(29.10.2011 23:00:00)
Sun 30 Oct(30.10.2011 22:00:00)
Mon 31 Oct(31.10.2011 22:00:00)
Tue 01 Nov(01.11.2011 22:00:00)

Answer 4

On my machine the output is:

root@ubuntu:~# php /tmp/tst.php
Mon 24 Oct
Tue 25 Oct
Wed 26 Oct
Thu 27 Oct
Fri 28 Oct
Sat 29 Oct
Sun 30 Oct
Mon 31 Oct
Tue 01 Nov
root@ubuntu:~# php -v
PHP 5.3.5-1ubuntu7.2 with Suhosin-Patch (cli) (built: May  2 2011 23:18:30)
Copyright (c) 1997-2009 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2010 Zend Technologies

what PHP version are you using?

Also, it might have something to do with daylight savings - try printing the hours too