session-php-examples-php-basic-9

  • Examples
  • Basic usage

  • Basic usage
  • Basic usage

    Basic usage

    Sessions are a simple way to store data for
    individual users against a unique session ID. This can be used to
    persist state information between page requests. Session IDs are
    normally sent to the browser via session cookies and the ID is used
    to retrieve existing session data. The absence of an ID or session
    cookie lets PHP know to create a new session, and generate a new
    session ID.

    Sessions follow a simple workflow. When a session
    is started, PHP will either retrieve an existing session using the
    ID passed (usually from a session cookie) or if no session is
    passed it will create a new session. PHP will populate the
    $_SESSION superglobal with any session
    data after the session has started. When PHP shuts down, it will
    automatically take the contents of the $_SESSION superglobal, serialize it,
    and send it for storage using the session save handler.

    By default, PHP uses the internal files save handler which is set by session.save_handler. This saves session data on the
    server at the location specified by the session.save_path configuration directive.

    Sessions can be started manually using the
    session_start() function. If the session.auto_start directive is set to 1, a session will automatically start on request
    startup.

    Sessions normally shutdown automatically when PHP
    is finished executing a script, but can be manually shutdown using
    the session_write_close() function.

    Example #1 Registering a variable with $_SESSION.

    <?php
    session_start
    ();
    if (!isset(
    $_SESSION['count'])) {
      
    $_SESSION['count'] = 0;
    } else {
      
    $_SESSION['count']++;
    }
    ?>

    Example #2 Unregistering a variable with $_SESSION.

    <?php
    session_start
    ();
    unset(
    $_SESSION['count']);
    ?>

    Caution

    Do NOT unset the whole $_SESSION with
    unset($_SESSION) as this will disable the registering of
    session variables through the $_SESSION superglobal.

    Warning

    You can’t use references in session variables as
    there is no feasible way to restore a reference to another
    variable.

    Warning

    register_globals will overwrite variables in the
    global scope whose names are shared with session variables. Please
    see Using Register
    Globals
    for details.

    Note:

    File based sessions (the default in PHP) lock the
    session file once a session is opened via session_start() or implicitly via session.auto_start. Once locked, no other script can
    access the same session file until it has been closed by the first
    script terminating or calling session_write_close().

    This is most likely to be an issue on Web sites
    that use AJAX heavily and have multiple concurrent requests. The
    easiest way to deal with it is to call session_write_close() as soon as any required
    changes to the session have been made, preferably early in the
    script. Alternatively, a different session backend that does
    support concurrency could be used.