A simple method to maintain current querystring when redirecting. Needed it for a WP plugin I'm making.

get_join.php

function get_join(){
	$keys = array_keys($_GET);
	$url = '?';
	$first = true;
	for($i = 0; $i < count($keys); $i++){
		if(!$first){
			$url .= '&';
		}
		$url .= $keys[$i].'='.$_GET[$keys[$i]];
		$first = false;
	}
	return $url;
}

Why bother with something this cumbersome and easily breakable?

function get_join() {
  return '?' . http_build_query($_GET);
}

I had no idea that function existed, I feel silly now :/