How to debug my PHP validation function?

Question

I am creating a web form for my work which is being validated using PHP. However, when I test the page I keep getting all of my error messages returned without the form being submitted properly when valid information is inputted. The following is a small section of the code (including the HTML sections).

<?php
$date =""
$dateerror = ""
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    if (empty($_POST["date"])) {
        $dateerror = "Date is required";
    } else {
        $date = test_input($_POST["date"]);
        $array = explode("/", $date);

        $day = $array[1];
        $month = $array[0];
        $year = $array[2];

        if (!checkdate($month, $day, $year)) {
            $dateerror = "Date mustbe in M/D/Y format";
        } else {
            date_default_timezone_set("America/Anchorage");
            $today = strtotime("now");
            if (strtotime($date)>=$today) {
                $date = test_input($_POST["date"]);
            } else {
                $dateerror = "Date is before present day";
            }
        }
    }

<input type="text" size="9" name="date" id="date" required title="Please enter current date"><?php echo $dateerror; ?><br>

Again, the PHP code just returns "Date is before present day" even when the date is the current date.

Answer 1

If you want to validate a date in PHP, the best way to do it is to use the DateTime class, and specifically the createFromFormat method.

This call will create a DateTime object set to the specified date in the given format, or false if it was an invalid date.

So for example:

<?php
$input = "05/08/2015";

$test = DateTime::createFromFormat('d/m/Y', $input);
if (!$test) {
    print "You entered an invalid date";
    die;
}

$now = new DateTime();
if ($test < $now) {
    print "Date is before present.";
    die;
}
?>

Simple as that. There's no need for regex, or for exploding the input, etc; just a single simple test. And you can also then use the $test variable to process the date as well once you've determined that it's valid, since it's a standard DateTime object.

[EDIT] I've added a bit in the code to deal with using the DateTime class to handle date comparisons, to give the 'before present' error.

The important point here is that if you have a DateTime object, you need to compare it with another DateTime object; the older strtotime() produces a different type of date resource to DateTime, and you can't use them together (at least not without converting between them all the time).