Undefined Index If I Do Not Check Checkbox

Question

I seem to have a bizarre happening here. If I check a checkbox on the form then the php script runs perfectly. If I don't check the box php reports an undefined index on another variable.

That's using IIS localhost, checking things.

On the web the published identical script works no matter what. Well, virtually identical. I have locally added a variable 'test' POST-ed to php and compared with a hard coded value. That's all.

Here's the html for the checkbox:

<tr>
<td>Publish Comment?</td>
<td><input name="publishok" value="NO" type="checkbox"> Check Box For Do spanstyle="font-weight: bold;">Not</span> Publish</td>
</tr>
<tr>

and here's the php for the variable, 'publishok' :

$IP = $_SERVER["REMOTE_ADDR"];
$publishok = $_POST['publishok'];
$test = $_POST['test'];
if ($test != 'park') die ("Wrong input. Sorry. Go back, try again");

I suspected my editor PSPad was adding spurious (and invisible) char codes or something so I upgraded to the latest version. No difference.

Can't think what could cause this.

Can anyone help?

But yeah, this is a quirk in the HTML/HTTP standard, from back when people cared about how long HTTP requests were. Someone thought "Hey, it's blank anyways, we don't need to tell them that, we can save a whole 3 bytes by not sending this information to them!" But you're far from the first or last person to get tripped up by this quirk. — Retsam
– Retsam, Commented Sep 4, 2013 at 1:32

xdazz · Accepted Answer · 2013-09-04 01:12:05Z

23

checkbox won't send the data to the server when you did not check it.

You have to use isset($_POST['publishok']) to check it whether it is checked in the server side.

answered Sep 4, 2013 at 1:12

xdazz

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totymedli · Accepted Answer · 2013-09-04 01:20:24Z

10

This happens because the checkbox's data isn't sent to the server if it is unchecked. A little hack for this is to use a hidden input field with the same name before the checkbox, so if the checkbox is unchecked, that value will be sent instead.

<input name="publishok" value="0" type="hidden">
<input name="publishok" value="NO" type="checkbox">

answered Sep 4, 2013 at 1:20

totymedli

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3 Comments

Retsam Over a year ago

Huh, this was the answer I was working on; but I didn't know you could just duplicate the name. I thought you had to set the hidden value using an onSubmit function or something like that...

user577111 Over a year ago

Well thanks for this. It got it working. But leaves me uncertain about checkboxes. I give it a value in the form in html - used to be 'NO' but now the value will be the zero of the hidden var if it is not checked. Right? So that'd be a 'zero'.

totymedli Over a year ago

@user577111 Yes it will be 0, but you can change it to anything you want. It can be NO too if you want that.

Class · Accepted Answer · 2013-09-04 01:12:47Z

5

I believe checkboxes and radio buttons don't send a get/post data if not selected/checked (you can verify this by doing a var_dump/print_r on $_GET/$_POST) so you should do something like:

if(isset($_POST['publishok'])){
    $publishok = $_POST['publishok'];
}else{
    $publishok = "";#default value
}

answered Sep 4, 2013 at 1:12

Class

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3 Comments

user577111 Over a year ago

Isset doesn't tell me what the value is. Only that there is one. Is that the heart of the matter? I should test like a Boolean? Expect a null as a 'negative' and (any) value as a 'positive'? But that throws the error I had and have fixed with the 'hidden' var. Very untidy isn't it? How should I set the box value in html and how should i test in php? Or should I use some other method?

Jodyshop Over a year ago

Thank you, should be the accepted answer. Working as expected.

Hotelsinger Over a year ago

Thank you for the complete answer. This is the one that helped fix my code.

Kwed · Accepted Answer · 2020-01-08 07:21:22Z

1

<input class="form-check-input" type="hidden" id="" name="check_box" value="0"> 

<input class="form-check-input" type="checkbox" id="gridCheck" name="check_box" value="1" 
<?php if ($_POST['check_box'] == "1") {
  print "checked";
 } ?>>

answered Jan 8, 2020 at 7:21

Kwed

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2 Comments

Guillaume Raymond Over a year ago

Here we like you explain in plain text why your code could solve the problem. Pllease take a momnet to consult the guide "How to write a good answer? " here stackoverflow.com/help/how-to-answer

Kwed Over a year ago

Create 2 input fields and make one hidden... Now add the value to the input fields This will solve the problem..

Ateeq Rafeeq · Accepted Answer · 2020-05-19 06:47:01Z

0

$_POST['wc_use_taxes'] = !isset($_POST['wc_use_taxes'])? "" : $_POST['wc_use_taxes'];

This code would set empty value in posted variable which isn't set and in case its set, that would make it equal to what posted. So i guess doing this would be good idea.

answered May 19, 2020 at 6:47

Ateeq Rafeeq

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