title: CodeIgniter 3 'Cannot modify header information' How to get error source
body: <p>I am using a multi users application running on a Wamp server 3.1.0. (PHP Version 7.1.22)</p>
  
  <p>Sometimes ,i get this error and i want to know which function or controller is causing this</p>
  
  <pre><code>ERROR - 2020-02-26 09:22:56 --&gt; Severity: Warning --&gt; Cannot modify header information - headers already sent by (output started at C:\wamp64\www\system\libraries\Session\Session_driver.php:49) C:\wamp64\www\system\core\Common.php 570
  ERROR - 2020-02-26 09:22:56 --&gt; Severity: Compile Error --&gt; Declaration of SessionHandlerInterface::close() must be compatible with SessionHandlerInterface::destroy($key) C:\wamp64\www\system\libraries\Session\Session_driver.php 49
  </code></pre>
  
  <p>I already changed log_threshold value to 1 to get error log, but i got same result</p>
  
  <pre><code>$config['log_threshold'] = 1;
  </code></pre>