php session variable undefine index

Question

I have two pages that i like to exchange variable. in the first page i have form like this:

<form method='post' action='rehabCreate2.php' onsubmit='return validateForm();'>
<input class="textbox" type='text' id='txt_stuNum' name='txt_stuNum'/ required>

<input type="submit" value="NEXT" id="btnNext">
</form>

then i set the session variable like this:

if ( isset( $_POST['btnNext'])){
$stuId=$_POST['txt_stuNum'];

$_SESSION["stuId"]=$stuId;
}

then in my page2 i want to it:

<?php
session_start();

$stuId=$_SESSION["stuId"];

echo $stuId;

?>

but it gives me error:

Notice: Undefined index: stuId in...

what am i missing? and another thing, how can i make a "back button" and the values are still in there?

EDIT: originally my "session_start()" was place at the top of the page1, but when i transfer it below my "" this error message show: Warning: session_start(): Cannot send session cache limiter - headers already sent (output started at C:\xampp\htdocs\cerecare\portal\somepage.php:176) in C:\xampp\htdocs\cerecare\portal\rehabCreate.php on line 16

by the way: the line 176 of somepage is the end of the script tag and nothing else follows

you miss to set $_SESSION["stuId"]=false; or something else on page1 when post not is set — donald123
– donald123, Commented Feb 4, 2015 at 8:35
did you forget to session_start(); in your $_POST processing page? — Ejaz
– Ejaz, Commented Feb 4, 2015 at 8:36
Does the page that sets the session variable also begin with session_start()? — James Hunt
– James Hunt, Commented Feb 4, 2015 at 8:37
Check page have session_start(). And you missed name attribute in submit button <input type="submit" value="NEXT" id="btnNext"> in this. Add name="btnNext" — Nes
– Nes, Commented Feb 4, 2015 at 8:37

Rakesh Sharma · Accepted Answer · 2015-02-04 08:42:03Z

1

First replace (give a name attr to submit button to get on POST)

<input class="textbox" type='text' id='txt_stuNum' name='txt_stuNum'/ required>
<input type="submit" value="NEXT" id="btnNext">

to

<input class="textbox" type='text' id='txt_stuNum' name='txt_stuNum' required />
<input type="submit" value="NEXT" id="btnNext" name="btnNext">

Add a session_start() on page1

session_start();
if (isset( $_POST['btnNext'])){
  $stuId=$_POST['txt_stuNum'];
  $_SESSION["stuId"] = $stuId;
}

Then Add a check for session value exist or not on page2

$stuId=(isset($_SESSION["stuId"]) ? $_SESSION["stuId"] :'');

edited Feb 4, 2015 at 8:42

answered Feb 4, 2015 at 8:36

Rakesh Sharma

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3 Comments

machineaddict Over a year ago

session_start() should always be the first line of code. Otherwise you could send something to output and you would get an error.

machineaddict Over a year ago

Also, as Nes pointed out, the submit button doesn't have a name, so the code in if condition will never get executed.

jaspher chloe Over a year ago

i try this but the second page is just blank.

M K Garwa · Accepted Answer · 2015-02-04 08:57:56Z

You forgot to add name for submit button but in addition whenever you are using any variable whether session or local variable just make sure it exists or not. so to save yourself from this problem always use this style of code given by @Rakesh Sharma.

 $var = isset($_SESSION['any_var']) ? $_SESSION['any_var'] : '';

or the better way to perform check and reduce calculation mistake use like this

$var = ( isset($_SESSION['any_var']) && !empty($_SESSION['any_var']) ? $_SESSION['any_var'] : '';

In statements also always use this style

if ( isset($_SESSION['any_var']) && !empty($_SESSION['any_var'])){
   /// code in statement
}

use this style of code always in your code and fee free at least from undefined index error and some calculation mistakes if value is empty.

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