如果尚未设置会话变量，则无法设置$ _SESSION变量

Question

I'm a bit stumped as for an answer to this one.

I have a registration form, and if there is a problem with a form input when it gets checked I'm saving a message to a session variable then checking to see if that session variable has anything it in and if it does, displaying the output at the top of my page I call session_start(); and when setting the message I use something like $_SESSION['msg'] = "Fill out all the information";

The problem I have however is that this only works when a user is logged in (IE a session has already been started) and when there is no session the $_SESSION['msg'] variable doesn't get set.

To check the error message I use this code.

        if(isset($_SESSION['msg'])){
            echo $_SESSION['msg'];
            unset($_SESSION['msg']);
        }

As you can see by the code at the top of the page, there is very little that sits between these. But there is a check done to see if the user has a valid session but all this does is either return true or false depending on how it evaluates, I've check it and it doesn't seems to be causing the problem as when I take it out, the issue still persists.

Can anyone shed some light on this problem?

session_start();
include_once("".$_SERVER['DOCUMENT_ROOT']."/includes/Krumo/class.krumo.php");
include_once("".$_SERVER['DOCUMENT_ROOT']."/auth/class_loader.php");
    $sessCheck = new userFunc;
    if($sessCheck->validSess('bool')){
        $sess = true;
    }
    else{ $sess = false;}


if(isset($_POST['email'])){
    if($_POST['email'] != NULL && $_POST['username'] != NULL && $_POST['pass'] != NULL && $_POST['rpass'] != NULL){
        $e = preg_replace('#[^a-z0-9_@.-]#i', '', $_POST['email']);
        if (!filter_var($e, FILTER_VALIDATE_EMAIL)) {
            $_SESSION['msg'] = "Please enter a valid email";
            return false;
        }
        else{

            $check = new userFunc;
            if($check->userExists($_POST['email'],$_POST['username'])){
                $_SESSION['msg'] = "An account with that email or username already exists";
                return false;
            }
            else
            {
                if(!$check->pswdMatch($_POST['pass'],$_POST['rpass'])){
                    $_SESSION['msg'] = "Passwords do not match";
                    return false;
                }
                $register = new register;
                $user = $register->startReg($_POST['username'],$_POST['email'],$_POST['pass']);
            }
        }
    }else
    {
        $_SESSION['msg'] = "Fill out all the information";
        return false;
    }
}

Answer 1

I have found what the issue was. Further down on my page I was building an account bar that sits in the top right of the page, this account bad uses the same $_SESSION['msg'] for the login form that sits in that bar at the top, and because there was a message set inside it, it was echoing out the message, then unsetting it, then reloading the page.