DateTime constructor in php

问题

I have done a little experiment on php's DateTime class. In the documentation they have suggested the syntax for creating the object of DateTime class as given.

Object oriented style:

public DateTime::__construct() ( [ string $time = "now" [, DateTimeZone $timezone = NULL ]] )

Procedural style:

DateTime date_create ( [ string $time = "now" [, DateTimeZone $timezone = NULL ]] )

Returns new DateTime object.

Here the first argument they have specified as mandatory, as a date/time string as specified in Date and Time Formats section. Or we have to pass NULL here to obtain the current time when using the $timezone parameter.

But my problem is when I am giving following code:

date_default_timezone_set('America/Los_Angeles');
$d_ob = new DateTime('x');
echo $d_ob->format('Y-m-d');

It's supposed to generate exception, but it's echoing the current date time like -

2013-09-29

I am not getting the point, how it's working?

回答1:

Apparently, this is not a bug, it is 'expected, but undocumented behaviour'^{See the comments to the bug report}. All single letters (except for 'j') represent military timezones, see some code to demonstrate this.

There is more information here.

From RFC822

The military standard uses a single character for each zone. "Z" is Universal Time. "A" indicates one hour earlier, and "M" indicates 12 hours earlier; "N" is one hour later, and "Y" is 12 hours later. The letter "J" is not used.

So to answer your question

I am not getting the point, how it's working?

When DateTime::__construct() is passed a single value that is not a valid time string it assumes that the first parameter has been omitted and tries to parse the string as a time zone. As the RFC explains, 'x' is a valid timezone, so you will get a DateTime instance that is in timezone 'X'.

I should mention that although the constructor of \DateTime recognises these single letter zones, the constructor of \DateTimeZone does not!

I hope that helps.

来源：https://stackoverflow.com/questions/19076825/datetime-constructor-in-php

标签

php

datetime

timezone