Question

How do you validate ISO 8601 date string (ex: 2011-10-02T23:25:42Z).

I know that there are several possible representations of ISO 8601 dates, but I’m only interested in validating the format I gave as an example above.

Answer 1

This worked for me, it uses a regular expression to make sure the date is in the format you want, and then tries to parse the date and recreate it to make sure the output matches the input:

<?php

$date = '2011-10-02T23:25:42Z';
var_dump(validateDate($date));

$date = '2011-17-17T23:25:42Z';
var_dump(validateDate($date));

function validateDate($date)
{
    if (preg_match('/^(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2}):(\d{2})Z$/', $date, $parts) == true) {
        $time = gmmktime($parts[4], $parts[5], $parts[6], $parts[2], $parts[3], $parts[1]);

        $input_time = strtotime($date);
        if ($input_time === false) return false;

        return $input_time == $time;
    } else {
        return false;
    }
}

You could expand further to use checkdate to make sure the month day and year are valid as well.