How to make sure a checkbox is checked?

**AJPayne** · August 23rd, 2004, 3:56 AM

Hi,

Well at the bottom of the form, I have the submit button. Just above it, I have a checkbox that is required to be checked in order to submit the form (It is just asking the user that they have read and agreed to the terms of use.) So I need it to be checked by the user.

So anyone know how to do this?

Thanks

H · August 23rd, 2004, 4:05 AM

Well, you give it a value right? If it's checked it has a value, otherwise it doesn't. You could do something like:

Code:

if ($checkbox==null) {
echo "Sorry checkbox blah blah blah";
} else{
echo "Hurray! You checked the box";
}

At least that's the way I remember it.. Think it's time for bed.

**Dave** · August 24th, 2004, 4:34 PM

I remember that $_POST['checkbox'] was set to either "on" or "off", but I don't really feel like validating that now.

**AngryPeasant** · August 24th, 2004, 7:14 PM

Your HTML checkbox code needs to look something like this:

Code:

<input type="checkbox" name="myCheckbox" value="123">

Haugland is right I think.
A checked checkbox will have the value specified by the value attribute.
An unchecked checkbox will be NULL (pretty sure, maybe not set... it will evaluate to FALSE either way...).

There's several ways you could write the conditional and make it work. Here's one way.

PHP Code:


			
if ( $_POST['myCheckbox'] == true )

  //checked

else

  //unchecked

**MrPixar** · August 24th, 2004, 8:36 PM

let's work on the example of:

Code:

<input type="checkbox" name="myCheckbox" value="123">

when you submit the form you will be able to access the value by simply using

Code:

$myCheckBox

Note: if the checkbox is UNchecked the variable will not exist. Haugland's code sample is correct

EDIT: I forgot to add that there is nothing wrong with using the

Code:

$_POST['myCheckbox']

method for retreiving variables from the query string, if you prefer but generally any variable data that gets posted from a form submit is directly available to PHP.

Hope that helps

Wolfy · August 25th, 2004, 5:26 AM

Quote:

Originally Posted by MrPixar

EDIT: I forgot to add that there is nothing wrong with using the

Code:

$_POST['myCheckbox']

method for retreiving variables from the query string, if you prefer but generally any variable data that gets posted from a form submit is directly available to PHP.

Hope that helps

Not only is there nothing wrong with use the $_POST, $_GET, $_COOKIE and $_REQUEST superglobal arrays to retrieve variable data from a form, URI or cookie but it is hugely preferrable if you intend on writing portable PHP scripts. The ability to "just use" variables specified by the POST or GET method relies on a PHP setting called register_globals which was changed to "off" by default in PHP 4.2 and above.

This means that any script NOT using the superglobal arrays may mysteriously fail to work on some servers.

Register globals was switched off by default because it represented a possible security risk due to mismanagement of variables. Details on the decision can be read here:

http://www.php.net/register_globals

-wolf

**patrickb** · August 25th, 2004, 5:47 AM

Wolfy is on the money here. Except, register_globals is on by default on all of our servers. Too many scripts break without it. I highly do not recommend the use of just $myCheckBox by itself. You should always explicitly specify where the variable is coming from (IE: $_POST['myCheckBox']). Many scripts have been hacked and exploited because they always assumed that the variables would be from the right place. Its a very poor coding practice that needs to be avoided (sorry MrPixar).

As far as the value, the variable itself will not even exist in the $_POST array if it wasn't check. So, a simple isset($_POST['myCheckBox']) call is all that is needed to verify if it was checked.

Wolfy · August 25th, 2004, 5:48 AM

There seems to be massive confusion over what is sent to the PHP script in the POST variable to represent a checkbox. To decode whats happening you need to know two things:

1) PHP does not know (or care) whether your form used a checkbox, radiobox, a textarea or your pet dog "Claudine". It ONLY knows what was passed in the URI.

2) The HTML code:

Code:

<input name="myCheckbox" value="YoMamma" type="checkbox"/>

Results in a URI of the form http://mydomain.com/myscript.php?myCheckbox=YoMamma if it is checked or http://mydomain.com/myscript.php if it is not checked.

THEREFORE, to discover whether the checkbox in the original form was checked we need to check for the existence of myCheckbox in the superglobal array as so:

PHP Code:


			
if (isset($_POST['myCheckbox'])) {

  // the checkbox was ticked; show sign up page

}

else

{

  // they didn't agree; prompt them

}

Something else occurs to me: as well as the PHP check something as simple as this could be checked using JavaScript. I recommend checking for these things both on the client side (using JavaScript) and on the server side (PHP). Not only does this provide a double check but it means that the user can be made aware of the problem without having to wait for the form to be submitted.

Sample code for checking whether a checkbox has been completed in JS below:

Code:

...
<head>
<script type="text/javascript" language="Javascript">
<!--
function checkForm() {
  if (document.getElementByID("agree").checked) {
    return true; // submit the form
  }
  else
  {
      alert("You must agree to our Terms of Service and Acceptable Use Policy.");
      return false;  // do not submit the form
  }
}
//-->
</script>
</head>
<body>
<form action="signup.php" method="post" onsubmit="checkForm();">
...
  <input name="agree" id="agree" type="checkbox" value="yes"/>
...
</form>
</body>
...

Hope this helps.

-wolf

Wolfy · August 25th, 2004, 5:51 AM

Ick. Patrickb beat me to the right answer before I could post!

Oh well; at least the JS might prove useful to someone else.

-wolf

August 23rd, 2004, 3:56 AM	#1 (permalink)
AJPayne I own you! Excelling Contributor Joined in Apr 2004 563 posts Gave thanks: 0 Thanked 3 times	How to make sure a checkbox is checked? Hi, Well at the bottom of the form, I have the submit button. Just above it, I have a checkbox that is required to be checked in order to submit the form (It is just asking the user that they have read and agreed to the terms of use.) So I need it to be checked by the user. So anyone know how to do this? Thanks

August 23rd, 2004, 4:05 AM	#2 (permalink)
H after g, before i Resident. Joined in Jul 2004 Lives in N,BC,CA 8,092 posts Gave thanks: 48 Thanked 131 times	Well, you give it a value right? If it's checked it has a value, otherwise it doesn't. You could do something like: Code: if ($checkbox==null) { echo "Sorry checkbox blah blah blah"; } else{ echo "Hurray! You checked the box"; } At least that's the way I remember it.. Think it's time for bed.

August 24th, 2004, 4:34 PM	#3 (permalink)
Dave Third Plateau Comfy Contributor Joined in Apr 2004 Lives in East Hanover, New Jersey Hosted on Nifty 272 posts Gave thanks: 0 Thanked 0 times	I remember that $_POST['checkbox'] was set to either "on" or "off", but I don't really feel like validating that now. __________________ site (syberdave.net) - server (nifty)

August 24th, 2004, 7:14 PM	#4 (permalink)
AngryPeasant Surpass Fan Seasoned Poster Joined in Aug 2004 Lives in North Carolina, USA Hosted on Pass11 46 posts Gave thanks: 0 Thanked 0 times	Your HTML checkbox code needs to look something like this: Code: <input type="checkbox" name="myCheckbox" value="123"> Haugland is right I think. A checked checkbox will have the value specified by the value attribute. An unchecked checkbox will be NULL (pretty sure, maybe not set... it will evaluate to FALSE either way...). There's several ways you could write the conditional and make it work. Here's one way. PHP Code: `if ( $_POST['myCheckbox'] == true ) //checked else //unchecked` __________________ All your base are belong to us.

August 24th, 2004, 8:36 PM	#5 (permalink)
MrPixar Pixel Smasher Comfy Contributor Joined in Feb 2004 Lives in Miami, FL Hosted on Pass51 139 posts Gave thanks: 0 Thanked 1 Time in 1 Post	let's work on the example of: Code: <input type="checkbox" name="myCheckbox" value="123"> when you submit the form you will be able to access the value by simply using Code: $myCheckBox Note: if the checkbox is UNchecked the variable will not exist. Haugland's code sample is correct EDIT: I forgot to add that there is nothing wrong with using the Code: $_POST['myCheckbox'] method for retreiving variables from the query string, if you prefer but generally any variable data that gets posted from a form submit is directly available to PHP. Hope that helps __________________ Pass51 \| garyzullo.com

August 25th, 2004, 5:47 AM	#7 (permalink)
patrickb the one who was Super #1 Joined in Jul 2003 Lives in Memphis 1,967 posts Gave thanks: 0 Thanked 3 times	Wolfy is on the money here. Except, register_globals is on by default on all of our servers. Too many scripts break without it. I highly do not recommend the use of just $myCheckBox by itself. You should always explicitly specify where the variable is coming from (IE: $_POST['myCheckBox']). Many scripts have been hacked and exploited because they always assumed that the variables would be from the right place. Its a very poor coding practice that needs to be avoided (sorry MrPixar). As far as the value, the variable itself will not even exist in the $_POST array if it wasn't check. So, a simple isset($_POST['myCheckBox']) call is all that is needed to verify if it was checked. __________________ Patrick Warnings: The program(s) might crash unexpectedly or behave otherwise strangely. (But of course, so do many commercial programs on Windows.) --www.gimp.org

August 25th, 2004, 5:48 AM	#8 (permalink)
Wolfy Registered User Seasoned Poster Joined in Jul 2004 31 posts Gave thanks: 0 Thanked 0 times	There seems to be massive confusion over what is sent to the PHP script in the POST variable to represent a checkbox. To decode whats happening you need to know two things: 1) PHP does not know (or care) whether your form used a checkbox, radiobox, a textarea or your pet dog "Claudine". It ONLY knows what was passed in the URI. 2) The HTML code: Code: <input name="myCheckbox" value="YoMamma" type="checkbox"/> Results in a URI of the form http://mydomain.com/myscript.php?myCheckbox=YoMamma if it is checked or http://mydomain.com/myscript.php if it is not checked. THEREFORE, to discover whether the checkbox in the original form was checked we need to check for the existence of myCheckbox in the superglobal array as so: PHP Code: `if (isset($_POST['myCheckbox'])) { // the checkbox was ticked; show sign up page } else { // they didn't agree; prompt them }` Something else occurs to me: as well as the PHP check something as simple as this could be checked using JavaScript. I recommend checking for these things both on the client side (using JavaScript) and on the server side (PHP). Not only does this provide a double check but it means that the user can be made aware of the problem without having to wait for the form to be submitted. Sample code for checking whether a checkbox has been completed in JS below: Code: ... <head> <script type="text/javascript" language="Javascript"> <!-- function checkForm() { if (document.getElementByID("agree").checked) { return true; // submit the form } else { alert("You must agree to our Terms of Service and Acceptable Use Policy."); return false; // do not submit the form } } //--> </script> </head> <body> <form action="signup.php" method="post" onsubmit="checkForm();"> ... <input name="agree" id="agree" type="checkbox" value="yes"/> ... </form> </body> ... Hope this helps. -wolf Last edited by Wolfy; August 25th, 2004 at 5:55 AM.. Reason: Added comment tags around JS to stop it showing in non-supporting browsers.

August 25th, 2004, 5:51 AM	#9 (permalink)
Wolfy Registered User Seasoned Poster Joined in Jul 2004 31 posts Gave thanks: 0 Thanked 0 times	Ick. Patrickb beat me to the right answer before I could post! Oh well; at least the JS might prove useful to someone else. -wolf

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