PHP XML Expat Parser
Parse XML documents efficiently with PHP's built-in Expat parser
📄 What is XML Expat?
XML Expat is a fast, event-based XML parser built into PHP. It reads XML documents sequentially and triggers functions when it encounters elements, making it memory-efficient for large files.
<?php
// Simple XML string
$xml = "<note><to>John</to><from>Jane</from></note>";
// Create parser
$parser = xml_parser_create();
echo "Parser created successfully!";
?>
Output:
Parser created successfully!
Key Expat Concepts
The Expat parser uses event-driven functions to process XML. You define handler functions that execute when the parser encounters specific XML structures like opening tags, closing tags, or character data.
Start Element
Triggered when opening tag found
function start($parser, $name, $attrs) {
echo "Start: $name";
}End Element
Triggered when closing tag found
function end($parser, $name) {
echo "End: $name";
}Character Data
Triggered for text content
function char($parser, $data) {
echo "Data: $data";
}Parser Setup
Configure and execute parser
xml_set_element_handler(
$parser, "start", "end"
);🔹 Creating an Expat Parser
Follow these steps to create and configure an XML Expat parser:
<?php
// Step 1: Create parser
$parser = xml_parser_create();
// Step 2: Define handler functions
function startElement($parser, $name, $attrs) {
echo "<b>Start tag: $name</b><br>";
}
function endElement($parser, $name) {
echo "<b>End tag: $name</b><br>";
}
function characterData($parser, $data) {
echo "Data: $data<br>";
}
// Step 3: Set handlers
xml_set_element_handler($parser, "startElement", "endElement");
xml_set_character_data_handler($parser, "characterData");
// Step 4: Parse XML
$xml = "<note><to>John</to></note>";
xml_parse($parser, $xml);
// Step 5: Free parser
xml_parser_free($parser);
?>Output:
Start tag: TO
Data: John
End tag: TO
End tag: NOTE
🔹 Parsing XML File
Read and parse XML from an external file:
<?php
// Create parser
$parser = xml_parser_create();
// Handler functions
function tagStart($parser, $name, $attrs) {
echo "Opening: $name<br>";
}
function tagEnd($parser, $name) {
echo "Closing: $name<br>";
}
// Set handlers
xml_set_element_handler($parser, "tagStart", "tagEnd");
// Open and parse file
$file = fopen("data.xml", "r");
while ($data = fread($file, 4096)) {
xml_parse($parser, $data, feof($file));
}
// Clean up
fclose($file);
xml_parser_free($parser);
?>Output:
Opening: BOOK
Closing: BOOK
Closing: CATALOG
🔹 Handling Attributes
Access XML element attributes in your handler functions:
<?php
$parser = xml_parser_create();
function startTag($parser, $name, $attrs) {
echo "Element: $name<br>";
if (!empty($attrs)) {
foreach ($attrs as $key => $value) {
echo "- Attribute: $key = $value<br>";
}
}
}
xml_set_element_handler($parser, "startTag", null);
$xml = '<book id="101" category="fiction"></book>';
xml_parse($parser, $xml);
xml_parser_free($parser);
?>Output:
- Attribute: ID = 101
- Attribute: CATEGORY = fiction
🔹 Error Handling
Detect and handle XML parsing errors:
<?php
$parser = xml_parser_create();
// Invalid XML (missing closing tag)
$xml = "<note><to>John</to>";
if (!xml_parse($parser, $xml)) {
echo "XML Error: " . xml_error_string(xml_get_error_code($parser)) . "<br>";
echo "Line: " . xml_get_current_line_number($parser);
} else {
echo "XML parsed successfully!";
}
xml_parser_free($parser);
?>Output:
Line: 1