php echo xml documents with header

Question

php code

<?php
$xml="<?xml version=\"1.0\" encoding=\"UTF-8\"?>";
$xml.="<db_entry id=\"$model->id\" doi=\"$model->identifier\">";
$xml.="<dataset>";
$xml.="</dataset>";
$xml.="</db_entry>";
$xml=preg_replace('/&(?!#?[a-z0-9]+;)/', '&amp;', $xml);
$output= simplexml_load_string($xml);
echo $output->asXML();

when i run it, it can't shows the xml format in the webpage(shows all text without xml tag). so i add the header(), but it shows XML Parsing Error: XML or text declaration not at start of entity.

<?php header("Content-type: text/xml"); ?>
<?php
    $xml="<?xml version=\"1.0\" encoding=\"UTF-8\"?>";
    $xml.="<db_entry id=\"$model->id\" doi=\"$model->identifier\">";
    $xml.="<dataset>";
    $xml.="</dataset>";
    $xml.="</db_entry>";
    $xml=preg_replace('/&(?!#?[a-z0-9]+;)/', '&amp;', $xml);
    $output= simplexml_load_string($xml);
    echo $output->asXML();

the webpage shows empty, but in the page view source it shows

<?xml version="1.0" encoding="UTF-8"?>
<db_entry id="5" doi="110039"><dataset/></db_entry>

and has three blank lines at the beginning.

Answer 1

Change this area

<?php header("Content-type: text/xml"); ?>
<?php
    $xml="<?xml version=\"1.0\" encoding=\"UTF-8\"?>";

To

<?php 
    header("Content-type: text/xml"); 
    $xml="<?xml version=\"1.0\" encoding=\"UTF-8\"?>";

REASON

By closing php in one line and opening again in the next line you are writing a line to the output. As you know, things outside <?php ?> tag will directly print to the browser. And as per XML rule, you cannot put anything before the <?xml ...?> part.

Answer 2

if you can try to print using this so that its work properly

echo '';print_r($output);echo '';die;