( [string id] )
session_id() returns the session id for the
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.
The constant SID can also be used to
retrieve the current name and session id as a string suitable for
adding to URLs. Note that SID is only defined if
the client didn't send the right cookie. See also Session handling.
See also session_start(),