php代码实现字符串的16进制编码解码

function hexEncode($s) {
return preg_replace('/(.)/es',"str_pad(dechex(ord('\\1')),2,'0',STR_PAD_LEFT)",$s);
}
function hexDecode($s) {
return preg_replace('/(\w{2})/e',"chr(hexdec('\\1'))",$s);
}
echo hexDecode(hexEncode("北京\n欢迎您！"));
?>