<?php
function arraytoxml($arr = array(),$charset=‘utf8‘) {  
$xml  =‘<!--xml version="1.0" encoding="‘.$charset.‘" -->‘;
$xml .= change($arr);
return $xml;
}
function change($source) {
$string="";
foreach($source as $k=>$v){
    $string .="<".$k.">"; 
    if(is_array($v) || is_object($v)){
        $string .= change($v);
    }else{ 
        $string .=$v;
    } 
    $string .="</".$k.">";
}
return $string;
}
 

$arr = array(
‘name‘ => array(
    ‘a‘ => ‘aa‘,
    ‘b‘ => ‘bb‘
)
);
$xml = arraytoxml($arr);
echo $xml;

<!--xml version="1.0" encoding="utf8" --><name><a>aa</a><b>bb</b></name>