Efficiency comparison of three methods for generating xml files in php

private function directWriteXml(&$data){
$xmltext='';
$xmltext .= '';
$xmltext .='';
$loop=count($data);
foreach ($data as $d){
$xmltext .=" ";
}
$xmltext .='';
$xmltext .=' ';
return $xmltext;
}
private function useDomDocument(&$data){
// Create an XML document and set the XML version and encoding. .
$dom=new DomDocument('1.0', 'utf-8');
// Create root node
$detail01 = $dom->createElement('Detail');
$dom->appendchild($detail01 );
foreach ($data as $d) {
$row = $dom->createElement('Row'," ID=" {$d['id']} " Name=" {$d['name ']}" " );
$detail01->appendchild($row);
}
return $dom->saveXML();
}
private function useSimpleXML(&$data){
// Create an XML Document and set XML version and encoding. .
$string = <<


XML;
$xml = simplexml_load_string ($string);
foreach ($data as $d) {
$xml->addChild('Row'," ID=" {$d['id']} " Name=" {$d['name ']}" " );
}
return $xml->asXML(); ;
}
?>

When calling, add a large number of loop operations to each one, and record the time .

$loop=10000;
$xml='';
switch($_GET['id']){
case 1:
$ts=$this->microtime_float( );
for( $i=0; $i<$loop; $i++)
$xml=$this->directWriteXml($depdata);
$te=$this->microtime_float();
$t =$te-$ts;
$this->assign('times',$t);
$this->assign('method','write directly');
break;
case 2:
$ ts=$this->microtime_float();
for( $i=0; $i<$loop; $i++)
$xml=$this->useDomDocument($depdata);
$te=$this- >microtime_float();
$t=$te-$ts;
$this->assign('times',$t);
$this->assign('method','DomDocument');
 break;
case 3:
$ts=$this->microtime_float();
for( $i=0; $i<$loop; $i++)
$xml=$this->useSimpleXML($depdata) ;
$te=$this->microtime_float();
$t=$te-$ts;
$this->assign('times',$t);
$this->assign('method ','SimpleXML');
break;
}
echo $xml;
?>

Actual test results: Direct writing is the fastest, and the time consumption is only about 1/3 of other methods. The other two methods are almost the same, and SimpleXML is faster in comparison.