PHP判断session是否开启

if (php_sapi_name() !=='cli') {
    if (version_compare(phpversion(), '5.4.0', '>=')) {
        session_status=== PHP_SESSION_ACTIVE?'':session_start();
    } else {
        session_id()===''?session_start():'';
    }
} else {
    session_start();
}