如何以HH：MM：SS格式添加两个日期字符串？

I am saving the variables in the format of HH:MM:SS. I want to sum up several variables such as:

TotalTime += var1+var2

It gives me the result of 0, whats the right format for getting the sum as HH:MM:SS?

This should work for you:

Here I just converted the first date into a DateTime object and the second date I converted into a DateInterval object, which I then can add() to the first date.

<?php

    $var1 = "12:23:01";
    $var2 = "05:22:45";

    $date = new DateTime($var1);
    list($hours, $minutes, $seconds) = explode(":", $var2);
    $interval = new DateInterval("PT" . $hours . "H" . $minutes . "M" . $seconds . "S");

    $date->add($interval);
    echo $date->format("H:i:s");

?>

output:

17:45:46