PHP 4, PHP 5, PHP 7, PHP 8
session_id - Get and/or set the current session id

session_id( [string|null$id = null] ): string|false

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 handling.



If id is specified and not null, 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)!


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.

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). On failure, false is returned.


Version Description
8.0.0 id is nullable now.

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