The primary purpose of the show_error() function in CodeIgniter is to display a detailed error message to the user when an exceptional situation occurs. It is particularly useful for providing users with clear and informative error messages, helping them understand what went wrong. Developers can customize the error message to include relevant details and instructions on how to resolve the issue, improving the overall user experience.

In CodeIgniter, the session ID regeneration interval is determined by the setting $config['sess_regenerate']. When set to 100, for example, the session ID will be regenerated every 100 requests, enhancing security by reducing the risk of session fixation attacks.

CodeIgniter's advanced database configuration enables the use of different database connections for reading and writing operations. This allows for optimization and control over database interactions based on the type of operation being performed.

Using stored procedures can enhance security by encapsulating SQL logic on the server side, reducing the risk of SQL injection attacks as user inputs are not directly embedded in the query.

The Query Builder in CodeIgniter helps prevent SQL injection by automatically escaping data used in queries. This means that user input is sanitized before being included in the SQL statement, reducing the risk of malicious SQL injection attacks. It adds a layer of security by handling the proper escaping of data, making the application more robust against common security threats.

Handling different API versions in CodeIgniter is commonly achieved through versioning. This involves incorporating the API version into the URI or request headers, allowing developers to make changes to the API without affecting existing clients.

The naming convention for custom library files in CodeIgniter is to use the format 'My_library.php' where 'My' is a user-defined prefix, and 'library' is the name of the library. This convention helps maintain consistency and avoid naming conflicts.

In CodeIgniter, data can be passed to a view by using the $this->load->view('view_name', $data) method, where 'view_name' is the name of the view file, and $data is an associative array containing the data to be passed.

The htmlspecialchars function in PHP is crucial for preventing XSS in user-generated content. It converts special characters to HTML entities, preventing the browser from interpreting them as code. This helps to neutralize potential XSS attacks.

The Email Class in CodeIgniter utilizes SSL Encryption for securing email communication. SSL (Secure Sockets Layer) is a cryptographic protocol that provides a secure channel for data transmission. In the context of email, it ensures that the email content is encrypted during transmission, enhancing the security of sensitive information.

In CodeIgniter, controllers can extend the core class CI_Controller for standard functionality. For more specialized functionality and to create a base controller with custom methods, you can create a new file named MY_Controller.php and extend CI_Controller.

CodeIgniter's database helpers primarily assist in creating and managing database connections. They simplify tasks related to database interaction in CodeIgniter, such as connecting to the database and executing queries.