Simple For-Loop results in memory exhausted error - php

Question

After working more than 4 hours on localizing the problem, I finally found the part of my code that leads to the following error:
PHP Fatal error: Allowed memory size of 268435456 bytes exhausted
(tried to allocate 8388608 bytes) in
I'm fetching data from my database. The query returns an array of data with 33 entries (not that much...)
I iterate over that array with a for-loop to get a time difference and flag the array if the difference is too big (simple if-else).... Its quite difficult to explain, but I guess you get what I mean by looking at my code... its pretty simple:
for($i = 0; $i <= count($customerList); $i++) {
$date1 = date_create($customerList[$i]["lastUpdate"]);
$interval = date_diff($date1, $date2);
$min=$interval->format('%i');
$sec=$interval->format('%s');
$hour=$interval->format('%h');
$mon=$interval->format('%m');
$day=$interval->format('%d');
$year=$interval->format('%y');
$date3 = date("H");
if(($year > 0) || ($mon > 0) || ($day > 0)) {
$customerList[$i]["flag"] = 1;
}
else {
if($date3 >= 6 && $date3 <= 21) {
if(($hour > 0) || ($min > 29)) {
$customerList[$i]["flag"] = 1;
}
}
}
}
The variable $date2 is defined before the for-loop with the following line of code:
$date2 = date_create($lastUpdateTime["lastUpdate"]);
Sadly I really don't see how this code can result in that error, since in my opinion this shouldn't really use that much memory...
Im 100 % sure that the error comes from this for-loop, since when I remove it the error is gone. Also, when I place this for-loop inside other views, it results in the same error.
I solved the problem by increasing the maximum memory limit of PHP, still I wonder how this for-loop can cause that problem.
I would really appreciate any explanations, since I don't find anything on the internet...
Oh, I'll just add the query here so you can see that I don't fetch a lot of data (the site handels much bigger queries without any problems...):
SELECT c.id, c.type, c.name, c.environment, cd.customer, MAX(cd.createdAt) AS lastUpdate FROM customerdata AS cd JOIN customers c ON cd.customer = c.id GROUP BY customer ORDER BY c.name ASC
Thank you!

Answer 1

Your for loop condition is $i<=count($customerList) instead of $i<count($customerList). This means your access of $customerList[$i] goes one past the end of the array, creating a new element along the way. Now count($customerList) is one larger, so the loop takes another iteration, ad infinum, thereby using more and more RAM for the growing array.
You should also get a warning message that the element does not (yet) exist when first accessing it, when you read "lastUpdate". Later, when you set the "flag" element, you create the array element.
To make the loop conditions easier to read and prevent typos like this, you could use a foreach loop:
foreach ($customerList as $customer) {
$date1 = date_create(customer["lastUpdate"]);
$interval = date_diff($date1, $date2);
...