session_id
  Get and/or set the current session id
  
 
  Description
  
   string session_id
    ([ string $id
  ] )
  
  
   The constant SID can also be used to
   retrieve the current name and session id as a string suitable for
   adding to URLs. See also Session
   handling.
  
  
 
  Parameters
  
   
    
     - 
id
- 
       
        If idis specified, it will replace the current
        session id. session_id needs to be called before
        session_start for that purpose. Depending on the
        session handler, not all characters are allowed within the session id.
        For example, the file session handler only allows characters in the
        range a-z A-Z 0-9 , (comma) and - (minus)!
 Note: 
        
         When using session cookies, specifying an idfor session_id will always send a new cookie
         when session_start is called, regardless if the
         current session id is identical to the one being set.
 
 
 
 
  Return Values
  
   session_id returns the session id for the current
   session or the empty string ("") if there is no current
   session (no current session id exists).