php undefined index notice not raised when indexing null variable

Question

I'm curious to know if the following behaviour in PHP is intended or not. And, if it is intended, it is considered acceptable to initialize an array from a null variable by creating an index into it (as is done in the first code snippet)?

error_reporting(E_ALL);
$arr = null;

echo ($arr["blah"]===null) ? "null" : $arr["blah"];

$arr["blah"] = "somevalue";
echo "<br>";
echo ($arr["blah"]===null) ? "null" : $arr["blah"];
var_dump ($arr);

This outputs

null
somevalue

array (size=1)
   'blah' => string 'somevalue' (length=9)

However, if the array is initialized first (see code below), I get the exact same output, but an "Undefined Index" notice is given when I first try $arr["blah"]

error_reporting(E_ALL);
$arr = array();

echo ($arr["blah"]===null) ? "null" : $arr["blah"];

$arr["blah"] = "somevalue";
echo "<br>";
echo ($arr["blah"]===null) ? "null" : $arr["blah"];
var_dump ($arr);

It is intended, but highly disrecommended. It's a relic of the past, not anything that should be used in good code. Always initialize your variables before use. — Waleed Khan
– Waleed Khan, Commented Nov 15, 2013 at 19:34
You should look into the functions isset(), is_null(), and empty(). Welcome to loosely-typed, implicit almost-everything hell. — Sammitch
– Sammitch, Commented Nov 15, 2013 at 19:40
I may not be understanding this question fully, however when "assigning", one would use the = operator instead of checking as a conditional statement of == or === am I missing something here? IMO, you can't pass off a conditional as an echo — Funk Forty Niner
– Funk Forty Niner, Commented Nov 15, 2013 at 19:46
@Fred-ii- those conditional checks are just for me for debugging to print out what's going on. the question is about why one can assign a value to an index of a variable that is null. Seems like a bad idea. $arr=null; $arr["index"] = "value"; — susie derkins
– susie derkins, Commented Nov 15, 2013 at 19:52
possible duplicate of Why does PHP not complain when I treat a null value as an array like this? — Chris Baker
– Chris Baker, Commented Nov 16, 2013 at 5:56

John Vargo · Accepted Answer · 2013-11-19 20:59:54Z

2

PHP won't attempt the comparison if the array is null.

In the second circumstance, a comparison does occur because the array is set. PHP does not check to see if it is empty.

Your ternary is attempting to access the variable $arr["blah"], not checking to see if it is set before doing a comparison.

The proper way to write this would be:

error_reporting(E_ALL);
$arr = array();

if(isset($arr["blah"])) echo ($arr["blah"]===null) ? "null" : $arr["blah"];

$arr["blah"] = "somevalue";
echo "<br>";
if(isset($arr["blah"])) echo ($arr["blah"]===null) ? "null" : $arr["blah"];
var_dump ($arr);

answered Nov 19, 2013 at 20:59

John Vargo

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Comments

Arjan · Accepted Answer · 2019-09-20 19:24:51Z

1

Actually, John Vargo was correct. If a variable is null, accessing it as if it were an array will simply return null without notices. This will change in the upcoming 7.4 version, then it will produce a notice.

Notice: Trying to access array offset on value of type null

The actual output is still the same.

answered Sep 20, 2019 at 19:24

Arjan

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