How to Add Two Date Intervals in PHP?

How to Add Two Date Intervals in PHP

PHP doesn't support operator overloading. Objects are first converted to strings when using the addition operator ( ). However, DateInterval doesn't support string conversion.

<code class="php">interval 1: 03:05
interval 2: 05:00
Total interval : 08:05</code>

Instead, create a new DateTime object, use the add() function to add the intervals, and calculate the difference to the reference point:

<code class="php">$e = new DateTime('00:00');
$f = clone $e;
$e->add($interval1);
$e->add($interval2);
echo "Total interval : " . $f->diff($e)->format("%H:%I") . "\n";</code>

Alternate Approach

Considering the internal storage structure of DateInterval, extending it and performing the calculation manually is also possible:

<code class="php">class MyDateInterval extends DateInterval
{
    public static function fromDateInterval(DateInterval $from)
    {
        return new MyDateInterval($from->format('P%yY%dDT%hH%iM%sS'));
    }
                                  
    public function add(DateInterval $interval)
    {
        foreach (str_split('ymdhis') as $prop)
        {
            $this->$prop += $interval->$prop;
        }
    }
}

$a = new DateTime('14:25');
$b = new DateTime('17:30');
$interval1 = $a->diff($b);
echo "interval 1: " . $interval1->format("%H:%I") . "\n";

$c = new DateTime('08:00');
$d = new DateTime('13:00');
$interval2 = $c->diff($d);
echo "interval 2: " . $interval2->format("%H:%I") . "\n";
                                  
$e = MyDateInterval::fromDateInterval($interval1);
$e->add($interval2);
echo "Total interval: " . $e->format("%H:%I") . "\n";</code>

Note: DateInterval extensions are possible with PHP extensions.

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