date_sub()

(PHP 5 >= 5.3.0, PHP 7)

别名DateTime::sub()

说明

此函数是该函数的别名：DateTime::sub()

It can be unclear for someone how to use this function.
Here is the example:
$date=date_create("2013-03-15");
date_sub($date,date_interval_create_from_date_string("40 days"));
echo date_format($date,"Y-m-d");

In version 5.6.31 the variable $ today is passed by reference in the function date_sub () and the interval is also applied
<?php 
$today = date_create(date('Y-m-d'));
$yesterday = date_sub($today, date_interval_create_from_date_string("1 days"));
    echo var_dump($today);
    echo var_dump($yesterday)
?>

To glue to the OOP, it's better to use it with DateInterval::createFromDateString
<?php 
$dateB = new DateTime('2020-12-20'); 
$dateA = $dateB->sub(DateInterval::createFromDateString('10 days'));
?>
more detail here :
<?php
public static function createFromDateString ($time) {}
?>

You cannot replace date_sub('2000-01-20') by DateTime::sub('2000-01-20') because DateTime::sub is not static. You have to create the DateTime object first.
Example:
<?php $dateA = date_sub('2000-01-20', date_interval_create_from_date_string('10 days')); ?>
will be replace by
<?php
$dateB = new DateTime('2000-01-20');
$dateA = $dateB->sub(date_interval_create_from_date_string('10 days'));
?>