Upgrading to PHP 5

Converting Between SimpleXML and DOM Objects

Using SimpleXML is usually easier than using DOM, but sometimes DOM’s comprehensiveness lets you do something that’s either hard or impossible in SimpleXML.

For example, you cannot discover the name of the root element in SimpleXML, but that’s no problem in DOM, as shown in Example 5-3.

Example 5-3. Converting between SimpleXML and DOM objects

$ab = simplexml_load_file('address-book.xml'); 

// Find the name of the root node 
$name = dom_import_simplexml($ab)->tagName; 

print $name;

address-book

SimpleXML gobbles up the root element, so there’s no way to derive its name using SimpleXML. However, the dom_import_simplexml( ) function takes a SimpleXML object and converts it to a DOM document. Under DOM, reference the object’s tagName property and you’re done.

These conversion features are particularly useful when you’re using SimpleXML as a generic XML document parser, because SimpleXML doesn’t really support XML document introspection. In contrast, DOM excels at this task.

Alternatively, you can perform the reverse transformation, as shown in Example 5-4.

Example 5-4. Converting between DOM and SimpleXML objects

$ab = new DOMDocument; 
$ab->load('address-book.xml');

// Find the email address of the first person
$email = simplexml_import_dom($ab)->person->email;

print $email;

[e-mail]

Use the simplexml_import_dom( ) function to turn a DOM object into a SimpleXML object.

Don’t worry about the performance overhead of these functions. Since SimpleXML ...