Do all header("Location: member.php?id=$username") have to be the first thing in a script? (PHP)

Question

I know in the Manuel it says that the header has to be the first thing in a script, but how come I see some codes where header("Location: member.php?id=$username") is in a if-statement?

Ex:

//a bunch of codes above

if($result!="0"){ 
// authenication correct lets login
$_SESSION["password"] = $password;;
$_SESSION["username"] = $username;
header("Location: member.php?id=$username");
}
else 
{
    echo "Wrong username or password. Please try again!";
}

But when I do this, it sometimes would/won't throw an error. How do I allow the header (); to be used in a script without any errors? I want to redirect the user back to the login if they click "no" and to the homepage if they click "yes".

Answer 1

It doesn't have to be the first thing in the script. But it haves to be the first thing that you output to the user. You MUST NOT echo stuff before using the header function. If you don't, you can use it at any place you want.

You could also "ignore output" using ob_start and ob_end_clean.

Best regards,
T.

Answer 2

You have to use output buffering so that nothing is sent back to the browser until the entire operation is complete. Check out the ob_start function, that should give you a good starting place.

ob_start

Without output buffering, the script sends header info back to the browser, and once that has happened you cannot use header() to redirect.

Answer 3

See my answer to a similar question.