does session_start have to be called inside every function?

Question

does session_start() have to be called within every function of a class? like:

class User {

  var $username;

  function set_session_username($username) {
    session_start();  # do I really need to call this again?
    $_SESSION['username'] = $username;
  }


  function retrieve_session_username() {
    session_start(); # do I really need to call this again?
    $this -> username = $_SESSION['username'];
  }

}

session_start();

$user = new User();
$user -> set_session_username('savagewood');
$user -> retrieve_session_username();

echo $user -> username;

Answer 1

No, it only needs to be called once per request. So the first script the runs post it at top of that file

Answer 2

No , you need to start the session only once in the page which is loaded. Not in any class or functions.

Answer 3

不，在应用程序发送任何输出之前，应该在应用程序入口点中调用一次session_start() 。

Answer 4

You could check if session is started:

if (!session_id())
  session_start();