Session Data Lost after redirection in Codeigniter

I am using Codeigniter 3.0.6 and PHP 7.1.2. Problem that I faced is the session data lost after redirecting to another controller. After googled, this issues is kind of a bug in Codeigniter. I have tried many solution found in google and this link gives the solution that works for my case.

I did exactly the steps that are shown in that link :

1. Go to system/libraries/Session/Session.php
2. Comment session_start() by adding //. We want to relocate the sessionn_start().
3. Find (using ctrl + f ) a comment that says "Security is king". Comment out all the line under that comment until the end of the function. In my case I commented out the line number 313 - 318.
4. Go to the main index.php, it is the first index.php and located in the same directory with the sub-directories 'application', 'system', 'user_guide', etc. 
5. Put 'session_start()' right after < ?php

Hope this can help you....

Cross-Origin Resource Sharing (CORS) Problem in Codeigniter

Facing a problem with CORS while developing a web with Codeigniter, the console keeps giving this error message "...has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource"

I browsed and tried many solutions posted in web, many failed to solve my problem. Finaly, I found a solution that works, at least for me. This is the link, where I found the solution. Link

So this is the solution:

Open "config.php" which is located in ../application/config/config.php .
Under Base Site URL, change existing configuration with this:

$config['base_url'] = ((isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] == "on") ? "https" : "http");
$config['base_url'] .= "://".$_SERVER['HTTP_HOST'];
$config['base_url'] .= str_replace(basename($_SERVER['SCRIPT_NAME']),"",$_SERVER['SCRIPT_NAME']);

This works like a charm....
Hope this can help you somehow...