What is PHP session_start() and session_destroy() function?

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PHP session_start() function is used to start the session. It starts new or resumes the current session. It returns the current session if the session is created already. If the session is not available, it creates and returns new sessions.

In a PHP interview, if you’re asked about session_start() and session_destroy() functions, you should be able to explain them in detail:

  1. session_start():
    • session_start() is a PHP function that initializes a session or resumes the current session based on a session identifier passed via a GET or POST request, or passed through a cookie.
    • It creates a session or resumes the current session if one exists. Sessions are a way to preserve data across subsequent HTTP requests.
    • This function must be called before any output is sent to the browser because it sends HTTP headers to set up a session cookie.
  2. session_destroy():
    • session_destroy() is a PHP function that destroys all data registered to a session.
    • It does not unset any of the global variables associated with the session, or unset the session cookie. So, after calling this function, the session still exists.
    • To completely remove session data, the session_unset() function should be called before session_destroy().
    • After destroying the session, the user will need to start a new session using session_start() if they want to use session variables again.

Here’s a concise example of how these functions might be used:

php
<?php
// Starting the session
session_start();

// Storing data in session variables
$_SESSION['username'] = 'john_doe';

// Destroying the session
session_unset(); // Unset all session variables
session_destroy(); // Destroy the session

// After session destruction, you might want to redirect the user or perform other actions.
?>

In this example, session_start() initializes the session, $_SESSION['username'] stores a value, and then session_unset() and session_destroy() remove the session data.