<?php
function curPageURL() {
 $pageURL = 'http';
 if ($_SERVER["HTTPS"] == "on") {$pageURL .= "s";}
 $pageURL .= "://";
 if ($_SERVER["SERVER_PORT"] != "80") {
  $pageURL .= $_SERVER["SERVER_NAME"].":".$_SERVER["SERVER_PORT"].$_SERVER["REQUEST_URI"];
 } else {
  $pageURL .= $_SERVER["SERVER_NAME"].$_SERVER["REQUEST_URI"];
 }
 return $pageURL;
}
?>

Test example:

<?php
  echo curPageURL();
?>

Source

1. Befriend the PHP Manual
If you're new to PHP, then it's time to get acquainted with the awesomeness that is the PHP manual. The PHP manual is incredibly thorough and has truly helpful comments following each article. Before asking questions or trying to figure out an issue on your own, save some time and just head straight to the manual. Odds are the answer to your question is already nestled in a helpful article at the PHP.net site. Read more..