# session_create_id

(PHP 7 >= 7.1.0)

session_create_id — Create new session id

### 说明

session_create_id ([ string `$prefix` ] ) : string

session_create_id() is used to create new session id for the current session. It returns collision free session id.

If session is not active, collision check is omitted.

Session ID is created according to php.ini settings.

It is important to use the same user ID of your web server for GC task script. Otherwise, you may have permission problems especially with files save handler.

### 参数

`prefix`

  If `prefix` is specified, new session id is prefixed by `prefix`. Not all characters are allowed within the session id. Characters in the range a-z A-Z 0-9 , (comma) and - (minus) are allowed.

### 返回值

session_create_id() returns new collision free session id for the current session. If it is used without active session, it omits collision check.

### 范例

Example #1 session_create_id() example with session_regenerate_id()

    <?php
    // My session start function support timestamp management
    function my_session_start() {
        session_start();
        // Do not allow to use too old session ID
        if (!empty($_SESSION['deleted_time']) && $_SESSION['deleted_time'] < time() - 180) {
            session_destroy();
            session_start();
        }
    }

    // My session regenerate id function
    function my_session_regenerate_id() {
        // Call session_create_id() while session is active to
        // make sure collision free.
        if (session_status() != PHP_SESSION_ACTIVE) {
            session_start();
        }
        // WARNING: Never use confidential strings for prefix!
        $newid = session_create_id('myprefix-');
        // Set deleted timestamp. Session data must not be deleted immediately for reasons.
        $_SESSION['deleted_time'] = time();
        // Finish session
        session_commit();
        // Make sure to accept user defined session ID
        // NOTE: You must enable use_strict_mode for normal operations.
        ini_set('session.use_strict_mode', 0);
        // Set new custom session ID
        session_id($newid);
        // Start with custom session ID
        session_start();
    }

    // Make sure use_strict_mode is enabled.
    // use_strict_mode is mandatory for security reasons.
    ini_set('session.use_strict_mode', 1);
    my_session_start();

    // Session ID must be regenerated when
    //  - User logged in
    //  - User logged out
    //  - Certain period has passed
    my_session_regenerate_id();

    // Write useful codes
    ?>

### 参见

- session_regenerate_id() - 使用新生成的会话 ID 更新现有会话 ID
- session_start() - 启动新会话或者重用现有会话
- session.use_strict_mode
- SessionHandler::create_sid() - Return a new session ID