Programming PHP

complex than it seems. The easiest and quickest solution is to use the XML parser
that ships with PHP.
PHP’s XML parser is based on the Expat C library, which lets you parse but not validate
XML documents. This means you can find out which XML tags are present and
what they surround, but you can’t find out if they’re the right XML tags in the right
structure for this type of document. In practice, this isn’t generally a big problem.
PHP’s XML parser is event-based, meaning that as the parser reads the document, it
calls various handler functions you provide as certain events occur, such as the
beginning or end of an element.
In the following sections we discuss the handlers you can provide, the functions to
set the handlers, and the events that trigger the calls to those handlers. We also provide
sample functions for creating a parser to generate a map of the XML document
in memory, tied together in a sample application that pretty-prints XML.
Element Handlers
When the parser encounters the beginning or end of an element, it calls the start and
end element handlers. You set the handlers through the xml_set_element_handler( )
function:
xml_set_element_handler(parser, start_element, end_element);
The start_element and end_element parameters are the names of the handler
functions.
The start element handler is called when the XML parser encounters the beginning of
an element:
my_start_element_handler(parser, element, attributes);
It is passed three parameters: a reference to the XML parser calling the handler, the
name of the element that was opened, and an array containing any attributes the
parser encountered for the element. The attribute array is passed by reference for
speed.
Example 11-2 contains the code for a start element handler. This handler simply
prints the element name in bold and the attributes in gray.
Example 11-2. Start element handler
function start_element($inParser, $inName, &$inAttributes) {
$attributes = array( );
foreach($inAttributes as $key) {
$value = $inAttributes[$key];
$attributes[] = "$key=\"$value\" ";
}
echo '<' . $inName . ' ' . join(' ', $attributes) . '>';
}
266 | Chapter 11: XML
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