PHP Undefined Variable, but it's defined and has a value - php

Question

I am working on a PHP project - I had one form post a date to another form
I made some changes (although none to the input in question)
Now all other inputs are updated with their Posted values, except the date
If I manually set the date in HTML it works:
<div><input type="date" class="form-control" id="DateCourse" name="DateCourse" value="2009-01-01"></div>
If I set it to the following, it doesn't:
<div><input type="date" class="form-control" id="DateCourse" name="DateCourse" value="<?php echo (isset($DateCourse))?$DateCourse:'';?>"></div>
The below:
$DateCourse = ($_POST["DateCourse"]);
var_dump($_POST["DateCourse"]);
var_dump($DateCourse);
Returns:
string(10) "2019-01-05" - means the post value is set
Notice: Undefined variable: DateCourse in /home/bitecons/bts.biteconsulting.co.za/v2/editccr.php on line 119 - how can it be undefined, I just defined it
NULL
What on earth am I doing wrong? Apart from using PHP :P
Flow as requested:
Records.php:
This is the function to prepopulate my posted fields:
function Prefill(x) {
TabletoEdit = x.closest('table').id;
SelectedRow = x.rowIndex;
document.getElementById("EntryEditing").value = x.cells[19].innerHTML;
document.getElementById("DateCourse").value = x.cells[0].innerHTML;
document.forms["records"].submit();
}
Then I also have:
<form action="editrec" method="post" id="records">
<input type='hidden' name='Period' id='Period' />
<input type='hidden' name='Month' id='Month' />
<input type='hidden' name='res' id='res' />
<input type='hidden' name='CustName' id='CustName' />
<input type='hidden' name='DateCourse' id='DateCourse' />
</form>
The Prefill gets called, then submits the form
I have tracked and DateCourse has data, but when getting to the other form, it "disappears":
if(!empty($_POST)) {
$DateCourse = ($_POST["DateCourse"]);
$CustName = ($_POST["CustName"]);
}
For example, CustName is filled in, but not DateCourse?
Side question:
Would this return true if another post var is not set (unrelated to this one):
if(!empty($_POST))

Answer 1

I think You use wrong Code
you Must Submit First Form And Then Use $DateCourse this In another Form in POSTBACK

Answer 2

One of the best way is to define $DateCourse too like
<?php
$DateCourse = "";
if(!empty($_POST["DateCourse"])) {
$DateCourse = ($_POST["DateCourse"]);
}
?>
<div><input type="date" class="form-control" id="DateCourse" name="DateCourse" value="<?php echo $DateCourse;?>"></div>

Answer 3

Okay, apologies folks, but it may help others in the future.
I had a function call to an old function - this failed, causing my variable to never get defined... I knew it was something stupid, but sometimes one needs a sound board...