(PHP 4, PHP 5, PHP 7)
session_id — Get and/or set the current session id
session_id() is used to get or set the session id for the current session.
SID can also be used to
retrieve the current name and session id as a string suitable for
adding to URLs. See also Session
id is 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.
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).