Warning: Undefined array key error in PHP

Question

This is my code:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>My First Form</title>
</head>
<body>
    <form action="form.php" method="get">
       Name: <input type="text" name="username">
        <br>
       Age: <input type="number" name="age"><br>
        <input type="submit">
    </form>

    <?php 
    echo $_GET["username"];
    echo "</br>";
    echo $_GET['age'];
    ?>
</body>
</html>

I'm getting an error:

Warning: Undefined array key "username" in C:\Users\nambi\Desktop\PHP Tutorial\form.php on line 18

Warning: Undefined array key "age" in C:\Users\nambi\Desktop\PHP Tutorial\form.php on line 20.

They are not set until you submit the form. Is that code in `form.php`? — brombeer, Jul 27 '21 at 08:55

Gerard de Visser · Accepted Answer · 2021-07-27T09:03:51.200

4

You should check first if the array key-value exists before you echo, like this:

<?php
if (isset($_GET["username"], $_GET["age"])) {
    echo $_GET["username"];
    echo "</br>";
    echo $_GET['age'];
}

edited Jul 27 '21 at 09:03

answered Jul 27 '21 at 08:55

Gerard de Visser

7,590
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needs an isset for the $_GET['age'] too – Gert B. Jul 27 '21 at 08:56
That would still show a `Warning: Undefined array key "age" ` – brombeer Jul 27 '21 at 08:56
`array_key_exists(..)` requires two parameters – brombeer Jul 27 '21 at 08:58
@brombeer he had isset() before the edit... that would do the trick :-) – Gert B. Jul 27 '21 at 08:59
Thx, was a bit to fast. Updatet my answer. – Gerard de Visser Jul 27 '21 at 08:59
1

@GertB. Yep, but now it is `array_key_exists()` - which doesn't do the trick ;) – brombeer Jul 27 '21 at 08:59
@GerarddeVisser I would use one if, so the unneeded
is removed too. – Gert B. Jul 27 '21 at 09:01
The difference between `isset` and `array_key_exists` is when a key exists with the value `null`, `isset` will return `false`, while `array_key_exists` will return `true`, so if the keys aren't set, before submit, both will return `false` – sschwei1 Jul 27 '21 at 09:03
Thx. I've adjusted my answer according to your comments. Feel free to vote ;) – Gerard de Visser Jul 27 '21 at 09:04
@sschwei1 using a form submit, the value will not be null – Gert B. Jul 27 '21 at 09:07
@GertB. exactly, so it doesn't matter whether to use `isset` or `array_key_exists`, or am I mistaken? – sschwei1 Jul 27 '21 at 09:10
2

@sschwei1 nope, but the answer is edited, he used array_key_exists() with only one param. and before that one he had isset(), so went from a working answer to a php error. (mistakes can happen). – Gert B. Jul 27 '21 at 09:14
@GertB. Ahh ok, haven't seen the edit before – sschwei1 Jul 27 '21 at 09:15
That's true. Didn't work after the first edit but works by now as answer is also accepted. – Gerard de Visser Jul 27 '21 at 09:21

Warning: Undefined array key error in PHP

1 Answers1