XML error at ampersand (&)

Question

I have a php file which prints an xml based on a MySql db.

I get an error every time at exactly the point where there is an & sign.

Here

Answer 1

$string = htmlspecialchars($string,ENT_XML1);

is the most universal way to solve all encoding errors (IMHO better that write custom functions + there is no point to solve just &).

Credit: Put Wrikken's and joshweir's comment as answer to be more visible.