Undefined Index in php: transfering variables from Ajax to php

Question

Hello I tried to transfer variable from ajax to php, but php file keeps throwing me the following:

Undefined index: vals in /Applications/XAMPP/xamppfiles/htdocs/fang_sophie/project/sign in-out/bin/readall2.php

Ajax reads like this:

<script>
var var_data = "Hello World";

$.ajax({ url: 'bin/readall2.php',
 data: {'vals' : var_data},
 type: 'post',
 dataType:'json',
 success: function(output) {
              alert(output);
          },
  error: function(request, status, error){
    alert("Error: Could not delete");
  }
});
</script>

Php reads like this:

<?php
  session_start();
  $hello = '';
  $_SESSION['hello'] = $_POST['vals'];
  echo($hello);
?>

Why doesn't it work? Please help :)

Answer 1

One problem here is that you're trying to output JSON dataType:'json', where you don't have JSON to start with. Consult my footnotes also.

You need to use a text data type.

dataType:'text',

By the way, this won't echo anything at all (in the alert), since $hello is empty:

session_start();
$hello = '';
$_SESSION['hello'] = $_POST['vals'];
echo($hello);

You (may) want to echo the session array taken from the POST array, which is the logical thing to do:

echo($_SESSION['hello']);

Reference:

• http://api.jquery.com/jquery.ajax/

---

Foonotes:

If by any chance you may be trying to access that (PHP) file directly, or your entire code is in the same file, then you need to use a conditional statement for it.

I.e.:

session_start();

if(!empty($_POST['vals'])){
    $hello = '';
    $_SESSION['hello'] = $_POST['vals'];
    echo($_SESSION['hello']);
}

That, and/or use two separate files.

In regards to JSON; if you really want/need to use it, then set it back to dataType:'json', but use json_encode() for it and replacing echo($_SESSION['hello']); with and assigning the $hello variable to the session array:

$hello = $_SESSION['hello'];
echo(json_encode($hello));

Answer 2

<?php
//first start session
session_start();

//set header to json and UTF-8 encoding
header('Content-Type: application/json;charset=utf-8');


//check if $_POST['vals'] is set first using isset() to prevent notice
//undefined index

if(isset($_POST['vals'])){
  echo "value of vals is: ".$_POST['vals'];
}else{
  echo "vals not set";
}
?>

Answer 3

The correct answer is you are reading the wrong variable:

$hello = '';
$_SESSION['hello'] = $_POST['vals'];
echo($hello);

It should be:

echo $_SESSION['hello'];

If you want the session data. For the undefined index, var_dump out your $_POST variable: var_dump($_POST);

If the $_POST variables do not match, or you get back an empty array, it was never transmitted to the server.

---

Original wrong answer:

When JQuery has "processData" flag set to false, it doesn't encode the data and requires the user reads it from the php://input stream.

Unencoded JSON is not sent into POST requests. For the quickest fix, try this:

parse_str(file_get_contents("php://input"), $vars);
// This will fill $vars with any data sent over to PHP.
var_dump($vars);

$vars should now be populated with the data you want. If $vars is empty, you are not transmitting the data.

Answer 4

In your ajax request, the format of return is expect to be JSON. and you are returning a string. You just need to add json_encode in your return line of php:

    session_start();
    $hello = '';
    $_SESSION['hello'] = $_POST['vals'];
    echo(json_encode($hello));