Manipulate a url string by adding GET parameters

Question

I want to add GET parameters to URLs that may and may not contain GET parameters without repeating ? or &.

Example:

If I want t

Answer 1

This function overwrites an existing argument

function addToURL( $key, $value, $url) {
    $info = parse_url( $url );
    parse_str( $info['query'], $query );
    return $info['scheme'] . '://' . $info['host'] . $info['path'] . '?' . http_build_query( $query ? array_merge( $query, array($key => $value ) ) : array( $key => $value ) );
}