Common session functions in PHP

1. Session_start ()
   
   This function indicates that the session needs to be used on this page. If this function is not used, other functions and session variables may fail to be used normally, similar to the initialization function.
2. Session_register ()
   
   This function is used to register a common variable as a session variable, as shown in figure
   
   $ A = 1;
   
   Session_register ("");
3. Session_unregister ()
   
   This function releases the registered session variable.
4. Session_is_registered ()
   
   Checks whether a specific session variable is registered and returns the bool type.
5. $ Http_session_vars ['varname']
   
   Used to obtain the value of the registered session variable. If the session is not registered, null is returned.