php: cannot modify array in function?

Question

so I am trying to modify an array by adding key and value in a function modArr; I expect the var dump to show the added items but I get NULL. What step am I missing here?

<?php

$arr1 = array();

modArr($arr1);
$arr1['test'] = 'test';
var_dump($arr);

function modArr($arr) {
    $arr['item1'] = "value1";
    $arr['item2'] = "value2";
    return;
}

Answer 1

You are modifying the array as it exists in the function scope, not the global scope. You need to either return your modified array from the function, use the global keyword (not recommended) or pass the array to the function by reference and not value.

// pass $arr by reference
$arr = array();
function modArr(&$arr) {
  // do stuff
}

// use global keyword
$arr = array();
function modArr($arr) {
  global $arr;
  //...
}

// return array from function
$arr = array();
function modArr($arr) {
  // do stuff to $arr
  return $arr;
}
$arr = modArr($arr);

To learn more about variable scope, check the PHP docs on the subject.

Answer 2

you have to pass $arr by reference: function modArr(&$arr)

edit: noticed an error in your code: you are passing modArr($arr1); but trying to output $arr