PHP $_SESSION Array Problem - php

Question

I am just trying to write a function in php that adds to the discount array but it doesn't seem to work at all.
function addToDiscountArray($item){
// if we already have the discount array set up
if(isset($_SESSION["discountCalculator"])){
// check that this item is not already in the array
if(!(in_array($item,$_SESSION["discountCalculator"]))){
// add it to the array if it isn't already present
array_push($_SESSION["discountCalculator"], $item);
}
}
else{
$array = array($item);
// if the array hasn't been set up, initialise it and add $item
$_SESSION["discountCalculator"] = $array;
}
}
Every time I refresh the page it acts like $_SESSION["discountCalculator"] hasn't been set up but I can't understand why. Whilst writing can I use the $_SESSION["discountCalculator"] in a foreach php loop in the normal way too?
Many thanks

Answer 1

The fact that every time $_SESSION['discountCalculator'] seems not to be set, could be because $_SESSION is not set (NULL). This case happens mostly when you did not executed session_start() at the beginning of you page.
Try adding session_start() at the beginning of the function.
function addToDiscountArray($item) {
if (!$_SESSION) { // $_SESSION is NULL if session is not started
session_start(); // we need to start the session to populate it
}
// if we already have the discount array set up
if(isset($_SESSION["discountCalculator"])){
// check that this item is not already in the array
if(!(in_array($item,$_SESSION["discountCalculator"]))){
// add it to the array if it isn't already present
array_push($_SESSION["discountCalculator"], $item);
}
}
else{
$array = array($item);
// if the array hasn't been set up, initialise it and add $item
$_SESSION["discountCalculator"] = $array;
}
}
Notice that this will not affect the function if the session is already started. It will only run ´session_start()` if the session is not started.