(PHP 4, PHP 5, PHP 7)
session_unset — Free all session variables
The session_unset() function frees all session variables currently registered.
   Returns TRUE on success or FALSE on failure.
  
| Version | Description | 
|---|---|
| 7.2.0 | The return type of this function is bool now. Formerly, it has been void. | 
Note:
If $_SESSION is used, use unset() to unregister a session variable, i.e.
unset ($_SESSION['varname']);.
    Do NOT unset the whole $_SESSION with
    unset($_SESSION) as this will disable the registering
    of session variables through the $_SESSION superglobal.
   
Note:
Only use session_unset() for older deprecated code that does not use $_SESSION.