append encoding on creation of xml file

this code creates an xml file if it does not exist:

$xmldoc = new DOMDocument();
    if(file_exists('test.xml')){
   开发者_开发问答 $xmldoc->load('test.xml');
    } else {
    $xmldoc->loadXML('<root/>'); 
    }

however, i would also like encoding="UTF-8" to be appended automatically on creation of the file. how would one do this in php?

To add/change the <?xml encoding value in the output of saveHTML(), you can set the encoding property.

$xmldoc->load('test.xml');
$xmldoc->encoding= 'utf-8';
$xmldoc->save('test.xml');

However, as Artefacto said, in this case it's pointless. An XML file without an <?xml encoding declaration or a UTF-16 BOM is definitely UTF-8 and all XML parsers will read it that way(*). You will gain nothing by adding an explicit encoding="utf-8" parameter to the XML Declaration.

Whatever the method is you're using to test, it's not doing what you think it's doing. Maybe you're loading XML into a text editor and it's saving it out in a different encoding, or something? You need to look at where you're getting the strings from that are going into the DOM before you save it, and if they're not UTF-8 you need to convert them then.

(*: Well unless it's served via another protocol with a higher-priority charset specification method, like HTTP's Content-Type header. But in that case the <?xml encoding declaration is ignored anyway.)

If you are trying to create a new UTF-8 encoded file, this should work:

$xmldoc = new DomDocument('1.0', 'UTF-8');
if(file_exists('test.xml')){
    $xmldoc->load('test.xml');
} else {
    $xmldoc->loadXML('<root/>'); 
}

But if you are opening a file that is not encoded in UTF-8, you'll have problems with the output... so you'll want to check the encoding of the file if it exists, and if not, you can create it as UTF-8.

OK:

<?php
    $xmlDoc = new DOMDocument('1.0', 'utf-8');
    print  $xmlDoc->saveXML();
?>

outputs:

<?xml version="1.0" encoding="utf-8"?>

The answer by bobince is correct and great help.
you can also read $dom->encoding from the file you read or grab.
I also output it with the header();

$xmldoc->load('test.xml');
$encoding = $dom->encoding;

/* ... manipulate dom ... */

header("Content-Type: application/xml; charset=". $encoding); 
echo $dom->saveXML();