DateTime::sub

date_sub

(PHP 5 >= 5.3.0)

DateTime::sub -- date_sub — Subtracts an amount of days, months, years, hours, minutes and seconds from a DateTime object

说明

面向对象风格

public DateTime DateTime::sub ( DateInterval $interval )

过程化风格

DateTime date_sub ( DateTime $object , DateInterval $interval )

Subtracts the specified DateInterval object from the specified DateTime object.

参数

object: 仅过程化风格：由 date_create() 返回的 DateTime 类型的对象。此函数会修改这个对象。
interval: A DateInterval object

返回值

返回被修改的 DateTime 对象，或者在失败时返回 FALSE.

范例

Example #1 DateTime::sub() example

面向对象风格


<?php
$date = new DateTime('2000-01-20');
$date->sub(new DateInterval('P10D'));
echo $date->format('Y-m-d') . "\n";
?>

过程化风格


<?php
$date = date_create('2000-01-20');
date_sub($date, date_interval_create_from_date_string('10 days'));
echo date_format($date, 'Y-m-d');
?>

以上例程会输出：

2000-01-10

Example #2 Further DateTime::sub() examples


<?php
$date = new DateTime('2000-01-20');
$date->sub(new DateInterval('PT10H30S'));
echo $date->format('Y-m-d H:i:s') . "\n";

$date = new DateTime('2000-01-20');
$date->sub(new DateInterval('P7Y5M4DT4H3M2S'));
echo $date->format('Y-m-d H:i:s') . "\n";
?>

以上例程会输出：

2000-01-19 13:59:30
1992-08-15 19:56:58

Example #3 Beware when subtracting months


<?php
$date = new DateTime('2001-04-30');
$interval = new DateInterval('P1M');

$date->sub($interval);
echo $date->format('Y-m-d') . "\n";

$date->sub($interval);
echo $date->format('Y-m-d') . "\n";
?>

以上例程会输出：

2001-03-30
2001-03-02

注释

DateTime::modify() is an alternative when using PHP 5.2.

参见

DateTime::add() - Adds an amount of days, months, years, hours, minutes and seconds to a DateTime object
DateTime::diff() - Returns the difference between two DateTime objects
DateTime::modify() - Alters the timestamp

PHP手册 - N: Subtracts an amount of days, months, years, hours, minutes and seconds from a DateTime object

用户评论:

Anonymous (01-Feb-2011 10:15)

Note that the sub() and add() methods will modify the value of the object you're calling the method on! This is very untypical for a method that returns a value of its own type. You could misunderstand it that the method would return a new instance with the modified value, but in fact it modifies itself! This is undocumented here. (Only a side note on procedural style mentions it, but it obviously does not apply to object oriented style.)

php at keith tyler dot com (01-Dec-2010 02:53)

If you use diff() after sub(), the effects of the sub() will be repeated on the date object. It doesn't matter if the object is the one diffed or doing the diffing (i.e. which object you call diff() from). <?php $today = new DateTime(); $newdate = new DateTime(); print_r($newdate); $newdate->sub(new DateInterval("PT1S")); print_r($newdate); $s = $newdate->diff($today); print_r($newdate); $s = $today->diff($newdate); print_r($newdate); $s = $today->diff($newdate); print_r($newdate); ?> Prints: DateTime Object ( [date] => 2010-11-30 18:43:48 [timezone_type] => 3 [timezone] => America/Los_Angeles ) DateTime Object ( [date] => 2010-11-30 18:43:47 [timezone_type] => 3 [timezone] => America/Los_Angeles ) DateTime Object ( [date] => 2010-11-30 18:43:46 [timezone_type] => 3 [timezone] => America/Los_Angeles ) DateTime Object ( [date] => 2010-11-30 18:43:45 [timezone_type] => 3 [timezone] => America/Los_Angeles ) DateTime Object ( [date] => 2010-11-30 18:43:44 [timezone_type] => 3 [timezone] => America/Los_Angeles ) Note that using add() instead of sub() does NOT have the same effect. This is particularly undesirable -- in this example you make a datetime, use sub() to make it a relative time in the past, and then date->diff() to confirm the difference. But the diff() inadvertendly makes the difference 2x.