从另一个日历时间减去一个日期时间并返回天数

I have 2 DateTime objects. One which represents 2 days from now and the other which represents 2 days and 6 months from now.

I need to be able to count the number of days between these two dates to display to users which dates they can book on.

I have calculated the two dates successfully but I am struggling finding a way to subtract them and return the difference in days.

$first; // first datetime object 
$second; // second datetime object 

$diff = $first->diff($second);

echo $diff->days;

Also take a look at DateInterval class at php.net

another way is:

$datetime1; //first date
$datetime2; //second date

$dayDiff = date_diff($datetime1, $datetime2);

echo $days;