Просто отредактируйте функцию выше, когда ключ является числовым, добавьте префикс «key_»
// initializing or creating array
$student_info = array(your array data);
// creating object of SimpleXMLElement
$xml_student_info = new SimpleXMLElement("<?xml version=\"1.0\"?><student_info></student_info>");
// function call to convert array to xml
array_to_xml($student,$xml_student_info);
//saving generated xml file
$xml_student_info->asXML('file path and name');
function array_to_xml($student_info, &$xml_student_info) {
foreach($student_info as $key => $value) {
if(is_array($value)) {
if(!is_numeric($key)){
$subnode = $xml_student_info->addChild("$key");
array_to_xml($value, $subnode);
}
else{
$subnode = $xml_student_info->addChild("key_$key");
array_to_xml($value, $subnode);
}
}
else {
if(!is_numeric($key)){
$xml_student_info->addChild("$key","$value");
}else{
$xml_student_info->addChild("key_$key","$value");
}
}
}
}