Undefined index: error

i am a beginner in php,i am facing a problem with the following code. it shows undefined index error."Undefined index: username in C:\wamp\www\phpmyadmin_practise\member.php on line 7 you must be login!".i can't understand what shoul 开发者_如何学编程i do.

session_start();
if($_SESSION['username'])
{
echo "Welcome,".$_SESSION['username']."!<br> <a href ='logout.php'> Logout </a> <br> <a href='changepassword.php'> changepassword </a> <br>";
}
else
{
    die("you must be login!");
}

?>

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username is not set. you should check variable with isset function before using them

if(isset($_SESSION['username']))

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If you open the page for the first time, $_SESSION['username'] will not be set (the key username does not exist). But you try to access it, so you get an error.

Use isset or array_key_exists:

if(isset($_SESSION['username']))

I hope you also have some kind of login page where the user is actually able to log in. die("you must be login!"); will terminate the current script. If this is the only page you have, $_SESSION['username'] will never be set.

And in production, you should not use die anyway. Create a proper error message on your page.

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$_SESSION['username'] is undefined. try this condition:

if(isset($_SESSION['username']))