title: Undefined PHP function filter_input
body: <p>I am trying to use the predefined function in PHP <code>filter_input</code></p>
  
  <p>But I get the following: <code>Call to undefined function filter_input()...</code></p>
  
  <p>The line it fails on is: <pre>$email = filter_input(INPUT_POST, 'email', FILTER_SANITIZE_EMAIL);</pre></p>
  
  <p>I can confirm there is a <code>$_POST['email']</code> that has a value and that I am using PHP 5.5.12 and the filter extension was enabled by default in 5.2.0 .</p>
  
  <p>I'm not sure what I am missing to access the function that should be already accessible.</p>
  
  <pre>
      $error_msg = "";
  
      if (isset($_POST['email'], $_POST['p'])) {
          // Sanitize and validate the data passed in
          $email = filter_input(INPUT_POST, 'email', FILTER_SANITIZE_EMAIL);
          $email = filter_var($email, FILTER_VALIDATE_EMAIL);
          if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
              // Not a valid email
              $error_msg .= 'The email address you entered is not valid</p>';
      }
  
          $password = filter_input(INPUT_POST, 'p', FILTER_SANITIZE_STRING);
      }
  </pre>
  
  <p>There isn't much code. It doesn't make it too far yet...</p>