session_id -- Get and/or set the current session id
string session_id ( [string id] )
session_id() is used to get or set the session id for
the current session.
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
If 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 and 0-9!
When using session cookies, specifying an id
for 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).