Months with less than 31 days omitted from list - php

Question

Consider the following code that was working perfectly yesterday, but now today (30th March), it has stopped working...
<form class="date">
<select name="date" onchange="this.form.submit()">
<?php
for ($i = 0; $i <= 60; ++$i) {
$time = strtotime(sprintf('+%d months', $i));
$value = date('Y-m', $time);
$label = date('F Y', $time);
$nowvalue = date('Y-m');
$nowlabel = date('F Y');
if(isset($_GET['date'])) {
if(strcmp($value,$_GET['date']) == 0) {
//If 0, $value and $_GET['date'] are the same: The option is selected
printf('<option value="%s" selected>%s</option>', $value, $label);
} else {
printf('<option value="%s">%s</option>', $value, $label);
}
} else {
if($value == $nowvalue) {
printf('<option value="%s" selected>%s</option>', $value, $label);
} else {
printf('<option value="%s">%s</option>', $value, $label);
}
}
}
?>
</select>
</form>
This outputs a select list of upcoming months, that onchange, reloads the page with a different query in the URL for the calendar on that page to react on.
If i manually update the query in the URL, it works fine, but this select list is repeating dates, have a look at the image below...
This cant be a coincidence that all of the months with the shortest days are missing, or in fact have been replaced with the same name as the month before?
Does anyone have an idea why this might be happening?

Answer 1

This is because when you loop through dates on a monthly basis on the 31st of the month you will come across months that have less than 30 days. PHP does automatically adjust the date to the last day of the month but instead goes to the end of the month and then adds the remaining days to it and gets the date that way which is the next month.
So if you get to February, which only has 28 days (most years) it will get to the 28th and add three days and give you March 3rd.
To solve this you need to set the date to the first day of the month and then iterate through the dates.

Answer 2

This is just an FYI as I realise that you've added your own answer.
You could instead use DateTime() to simplify your code (if you want).
So you could end up with something like:
<select name="date" onchange="this.form.submit()">
<?php
$selected = DateTime::createFromFormat('Y-m-d', #$_GET['date'] . '-01') ?: new DateTime('first day of this month');
for ($i = 0; $i <= 60; $i++) {
$date = (new DateTime('first day of this month'))->modify("+$i months");
$select = $date == $selected ? 'selected' : '';
printf('<option value="%s" %s>%s</option>', $date->format('Y-m'), $select, $date->format('F-Y'));
}
?>
</select>
Hope this helps!

Answer 3

As John Conde pointed out, this is because todays dates (the 31st) plus one month is actual May 1st, and April is skipped.
I did the following to set the date to the 1st of the month, then plus one month...
<?php
for ($i = 0; $i <= 60; ++$i) {
$firstofthismonth = '01-' . date('m-Y');
$time = strtotime(sprintf($firstofthismonth . '+%d months', $i));
$value = date('Y-m', $time);
$label = date('F Y', $time);
$nowvalue = date('Y-m');
$nowlabel = date('F Y');
if(isset($_GET['date'])) {
if(strcmp($value,$_GET['date']) == 0) {
//If 0, $value and $_GET['date'] are the same: The option is selected
printf('<option value="%s" selected>%s</option>', $value, $label);
} else {
printf('<option value="%s">%s</option>', $value, $label);
}
} else {
if($value == $nowvalue) {
printf('<option value="%s" selected>%s</option>', $value, $label);
} else {
printf('<option value="%s">%s</option>', $value, $label);
}
}
}
?>