PHP - session variable cannot be set

Question

I wrote a page 'captcha.php' to generate a math captcha and send the result through session to the page which request it.
In captcha.php:

$_SESSION['captcha'] = $var;//$var is the calculate result

In index.php:

<img src="/captcha.php"/><input id="captchaa" type="text" name="a"/>
...
<?php    
if($_POST['a']==$_SESSION['captcha'])
...

But I got 'Undefined index: captcha' error.
Any hint? Or what else more information do you need?

UPDATE: these lines are in both files if(!isset($_SESSION)) { session_start(); }

UPDATE: I think i found the reason. My index.php is in the frame of Yii, and it has a session with id, but the captcha.php is not within the framework, so they cannot share a session.I tried to make it a view(/validation/captcha ),but it won't generate image properly that way, don't know why.

Now the problem is how to use Yii's session in captcha.php.

heximal · Accepted Answer · 2011-09-09 08:31:52Z

2

did you use the session_start function in both your files?

edited Sep 9, 2011 at 8:31

heximal

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answered Sep 9, 2011 at 8:31

mishu

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3 Comments

mishu Over a year ago

Also keep in mind that if you set the session var in captcha.php and you use that file to render that image also, considering that the image is shown before you check the answer received, the value saved in your session will be changed at the time of your check

dotslashlu Over a year ago

if(!isset($_SESSION)) { session_start(); }is in both of the two files.

dotslashlu Over a year ago

I think i found the reason. My index.php is in the frame of Yii, and it has a session with id, but the captcha.php is not within the framework, so they cannot share a session.I tried to make it a view(/validation/captcha ),but it won't generate image properly that way, don't know why. Now the problem is how to use Yii's session in captcha.php.

J0HN · Accepted Answer · 2011-09-09 09:09:13Z

1

It's because captcha.php is processed in a separate request by browser. So, the flow is the following:

PHP executes index.php file. NO $_SESSION['captcha'] is set, so nothing is outputted
PHP flushes the content to the browser.
Browser sees src parameter of the img and loades that url
PHP executes captcha.php and sets $_SESSION['captcha'], but the page is already rendered.

So, actually your $_SESSION['captcha'] is set after the index.php is processed and even after another HTTP request.

As a workaround you may use AJAX loading captcha, passing both captcha value and image via AJAX request and than injecting them into HTML page.

answered Sep 9, 2011 at 9:09

J0HN

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Comments

Stefan H Singer · Accepted Answer · 2011-09-09 08:32:13Z

0

Hard to tell without seeing the rest of captcha.php, have you called session_start() before setting the session variable?

answered Sep 9, 2011 at 8:32

Stefan H Singer

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Comments

Jonnix · Accepted Answer · 2011-09-09 08:34:16Z

0

The variable $_SESSION['captcha'] will not be available in index.php until the next page load as it is being created in a request after the one you are currently in, if that make sense.

Checking if the form has been submitted /then/ checking the value against the $_SESSION should work as long as session_start() is being used correctly.

answered Sep 9, 2011 at 8:34

Jonnix

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Comments

heximal · Accepted Answer · 2011-09-09 08:36:07Z

0

I agree with mishu about session_start. 'Undefined index: captcha' is not an error. It's rather a warning. If you don't suppress the output of warning messages, you should check if specified array index really exists:

if(isset($_POST['a']) && isset($_SESSION['captcha'])&&$_POST['a']==$_SESSION['captcha'])
...

to suppress warnings output you should use error_reportning function, if it's not critical to you.

answered Sep 9, 2011 at 8:36

heximal

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1 Comment

dotslashlu Over a year ago

I did as you've said and the procedure was also post then check, but var_dump($_SESSION['captcha']) is always NULL

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