Question

I have a form with multiple checkboxes, which I want to put into an array. I go by the example provided here: http://www.kavoir.com/2009/01/php-checkbox-array-in-form-handling-multiple-checkbox-values-in-an-array.html

So I’ve prepared the files:

checkboxes.php:

<form action="checkboxes2.php" method="post">
<input type="checkbox" name="tags[]" value="1" />1<br>
<input type="checkbox" name="tags[]" value="2" />2<br>
<input type="checkbox" name="tags[]" value="3" />3<br>
<input type="checkbox" name="tags[]" value="4" />4<br>
<input type="submit" value="Send" />
</form>

checkboxes2.php:

<?php
print_r($_POST["tags"]);
?>

Pretty simple…I realize I should only get the value of these textboxes and not if they have been selected or not. But I still get this error:

Undefined index: tags in checkboxes2.php on line 2

I have absolutely no idea what I did wrong here. I went by the example in the link above and did everything exactly the same (mainly copy/pasting and changing some parts like adding a submit button) but I don’t get the output as shown in the example. I should at least get the values of each of these checkboxes, right?

What I want to do: I want to check the array of checkboxes, see which ones have been selected and add “yes” or “no” into a second array, like this:

<?php
  $number1 = $_POST["tags"];
  $number2 = array();

  foreach($number1 as $number1_output)
  {
    if(isset($number1_output))
    {
      $number2[] = "yes";
    }
    else
    {
      $number2[] = "no";
    }
  }

  print_r($number2);
?>

Well…it only half works. Only the checkboxes that have been selected are added to the array. So if I select “3” and “4” I get this:

Array ( [0] => yes [1] => yes )

What is the best way to deal with checkboxes in arrays and validating them?

Answer 1

Alternatively, if you want to have checkboxes that also send a value if they are not checked, you can add a Hidden input field before the checkbox:

<input type="hidden" name="tag[1]" value="off" />
<input type="checkbox" name="tag[1]" value="on />

Because the checkbox is only sent if it is set, but it overrides the hidden as it is later in the HTML, you will now always have tag[1] set with either ‘off’ or ‘on’ depending on whether or not the box was checked.