filter_has_var

Please note that the function does not check the live array, it actually checks the content received by php:

<?php
$_GET['test'] = 1;
echo filter_has_var(INPUT_GET, 'test') ? 'Yes' : 'No';
?>

would say "No", unless the parameter was actually in the querystring.

Also, if the input var is empty, it will say Yes.

Through this example i think you can better understand

    if ( !filter_has_var(INPUT_GET, 'email') ) {
        echo "Email Not Found";
    }else{
        echo "Email Found";
    }
    Output

    localhost/nanhe/test.php?email=1 //Email Found
    localhost/nanhe/test.php?email //Email Found
    http://localhost/nanhe/test.php //Email Not Found

Consider on second example

http://localhost/nanhe/test.php
$_GET['email']="info@nanhe.in";
if ( !filter_has_var(INPUT_GET, 'email') ) {
        echo "Email Not Found";
    }else{
        echo "Email Found";
    }
But output will be Email Not Found