Php -- quick explanation how to use webpage.php?error=1 - php

Question

I can't find this anywhere right now and looking for a quick answer.
What is the functionality of using webpagename.php?error=1?
Basically I want to use it so that when an error occurs logging in, I can redirect them to the page with a different message saying error.
I tried using
header('Location: loginpage.php');
echo '<p class="error">Error Logging In!</p>';
but nothing ever shows up. Thanks!

Answer 1

in two way you can do this!
-1:
use like that parameter in URL
header('Location: loginpage.php?error=1');
in loginpage.php in JavaScript section check URL is contain error or not!
look at this link
just replace "q" with error!
make a function and check if contain error
show a error message!
<script>
function logincheck(){
// code
}
if(logincheck()){
// do something
//alert('error');
// or append a error in html element
}
</script>
you can check this query string in php but JavaScript way is better
-2
use session
after validate set a session with error message
like this:
$_SESSION['login_error'] = 'error in login!';
and in loginpage.php
check if that session have a value, show that to user,and unset session
like this:
if(isset($_SESSION['login_error'])){
echo '<p class="error">Error Logging In!</p>';
unset($_SESSION['login_error']);
}

Answer 2

when u doing header, you already redirecting to the loginpage.php
you should put the error message at loginpage.php.
or you can hold the redirection by doing something like
header('Refresh: 3;url=loginpage.php');
which redirect after 3 second;

Answer 3

On the page processing the login check, if login fails:
header('Location: loginpage.php?error=1');
Inside of loginpage.php place code where you want the message to appear:
<?php
If ($_GET['error']==1) {echo "login error!"} elseif ($_GET['error']==2) { echo some other message } .....
?>
The purpose of ?error=1 in the url is to pass a variable named ERROR with a value of 1 through the URL which is accessable to the redirection target page through $_GET