Undefined array in php

Question

Form code

<form action=<?=$_SERVER['PHP_SELF']?> method="POST" id="form1">
Enter length of password:<input type="text" name="length">
<input type="submit" value="Submit"/>

PHP code

    <?php 
    $length=$_POST['length']
    ?>

Error:

Undefined array key "length" in D:\XWAMP\htdocs\pg\index2.php on line 30

I'm writing both html and php in single file that's why it's happening but how to handle it?

Arischvaran · Answer 1 · 2022-01-02T12:15:24.357

1

I assume the web page loads and you get the error. In this case, you haven't check whether the form is submitted. Before the form is submitted you also haven't added a name for your submit button.

if(isset($_POST['submit'])){
    $length = $_POST['length'];
}

This should solve your problem I suppose. A similar question was asked here: Check if form was submitted

edited Jan 02 '22 at 12:15

answered Jan 02 '22 at 12:08

Arischvaran

74
4

Right idea, but $_POST['submit'] won't be set in this case, because the button in the OP's form has no name – ADyson Jan 02 '22 at 12:11
I think you forgot "))" in the first line – François Huppé Jan 02 '22 at 12:14
@ADyson you're right. – Arischvaran Jan 02 '22 at 12:16
1

@FrançoisHuppé lol thanks man. – Arischvaran Jan 02 '22 at 12:17
why not simply if(isset($_POST['length'])){ ... – François Huppé Jan 02 '22 at 12:17
Well then you'd have to do that if for every attribute you have say name, username, password, phone number and who knows what else you might have. The code then becomes really messy in my opinion. – Arischvaran Jan 02 '22 at 12:19
you're right... – François Huppé Jan 02 '22 at 12:23

score 0 · Answer 2 · answered Jan 02 '22 at 12:22

Various issues,

action=<?=$_SERVER['PHP_SELF']?> is open to XSS don't use it
To check if its POST request, use $_SERVER['REQUEST_METHOD'] === 'POST'
Always validate user input and respond in kind to the user

<?php
$errors = [];
if ($_SERVER['REQUEST_METHOD'] === 'POST') {
   // validate length
   if (!isset($_POST['length'])) {
     $errors['length'] = 'Length is a required field';
   } else if (!is_numeric($_POST['length'])) {
     $errors['length'] = 'Length should be a number';
   } else if ($_POST['length'] < 1) {
     $errors['length'] = 'Length should be a >= then 1';
   } else if ($_POST['length'] > 1000) {
     $errors['length'] = 'Length should be a <= then 1000';
   }

   // no errors, do processing on length
   if (empty($errors)) {
      $length = $_POST['length'];

      // do something with $length
   }
} 
?>

<form action="" method="POST" id="form1">
  Enter length of password: 
  <input type="text" value="<?= isset($_POST['length']) ? htmlentities($_POST['length']) : '' ?>" name="length" required>
  <?= isset($errors['length']) ? '<div class="input-error">'.$errors['length'].'</div>' : '' ?>
  
  <input type="submit" value="Submit"/>
</form>

Undefined array in php

2 Answers2