1 days equals 86,400 seconds?

Date arithmetic is often used in writing code. Most of the time, for convenience, it is possible to simply add and subtract a timestamp:

$time = mktime (0, 0, 0, 8, _hour_later); $one = Date (' y-m-d h:i:s ', $time + 3600);

This is a simple code to get a timestamp after an hour, but if you zoom in to a unit above the day, is this timestamp really what you want?

For example, if you have a time stamp of 0 o ' Day, you want to know the time stamp of 0 o ' day after 5 days, simply add the time after 5*86400?

>> 2015-03-13 00:00:00

There seems to be no problem. But what about the people in a different place?

The time zone is set to Chicago Date_default_timezone_set (' America/chicago '); $time = mktime (0, 0, 0, 3, 8); $five _day_later = Date (' Y-m-d h:i:s ', $time + 5 * 86400); echo $five _day_later;

>> 2015-03-13 01:00:00

Why isn't it 0 o ' day after 5 days?

Of course, this key problem is in daylight saving time (the principle of specific daylight savings is not introduced, can be self-Baidu).

Workaround: Use the Strtotime function instead of adding and subtracting

The time zone is set to Chicago Date_default_timezone_set (' America/chicago '); $time = mktime (0, 0, 0, 3, 8); $five _day_later = Date (' Y-m-d h:i:s ', Strtotime (' +5 days ', $time)); Echo $five _day_later;

>> 2015-03-13 00:00:00

While this problem does not exist in time zones that do not have daylight savings, it does affect your expected results for time zones that have daylight savings.

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