ajax and php undefined index

Question

Here is my ajax code:

function send()
{
    var xmlhttp;
     if (window.XMLHttpRequest)
       {// code for IE7+, Firefox, Chrome, Opera, Safari
       xmlhttp=new XMLHttpRequest();
       }
     else
       {// code for IE6, IE5
       xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
       }

    xmlhttp.onreadystatechange=function()
       {
       if (xmlhttp.readyState==4 && xmlhttp.status==200)
         {
            alert(xmlhttp.responseText);
         }
       }

    xmlhttp.open("POST","test.php",true);
    xmlhttp.send('subject=' + document.getElementById("subject").value);
}

here is my php code:

<?php
$subject = $_POST['subject'];
echo $subject;
?>

It says error on line 2 in the php code, undefined index. I don't know what else to do..any help would be apriciated, thanks.

an obvious comment, but does your form element definitely have the id subject? I would also try it with GET instead, worth a try! — martincarlin87
– martincarlin87, Commented Jan 19, 2012 at 16:16

Dan Prince · Accepted Answer · 2012-01-19 15:55:51Z

1

This means that there is no 'subject' value in the $_POST array. This means that when the request to the page was made, there was not a post variable called subject with a value. One simple way to check for this is to use:

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

This was makes sure that subject has a value and will not cause any page errors. Make sure you are definitely sending a POST variable called subject (You can do this in Chrome Developer tools or Firebug in the Network requests panel).

answered Jan 19, 2012 at 15:55

Dan Prince

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9 Comments

user1104615 Over a year ago

Got it, but whats the problem? why it isn't getting the value of subject?

Dan Prince Over a year ago

As I said, if this is an AJAX application, then check your network panel in dev tools or firebug and look at the request data, in the header it should show the request variables and their type. Check that there is a POST variable being sent, and that it has the value you are expecting it to.

user1104615 Over a year ago

Firebug in post: Source subject=dfgasdasd Firebug in response: Notice: Undefined index: subject in C:\wamp\www\msgs\test.php on line 2 ???

Dan Prince Over a year ago

Try it with GET instead, see if you have the same problem.

Dan Prince Over a year ago

Try it with $_POST again and use: print_r ( $_POST ); You should be able to see the variables that are in the post array.

|

mustafa · Accepted Answer · 2012-01-19 15:54:14Z

0

Check your form input named subject. You might have misspelled it.

answered Jan 19, 2012 at 15:54

mustafa

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2 Comments

user1104615 Over a year ago

Nope..I get the value of the subject, tested it.

MetalFrog Over a year ago

If 'subject' was in your $_POST, you wouldn't have the notice about the undefined index.

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