Introduction: Why Use PHP XML Expat?

When you’re dealing with large XML files or real-time XML streams (like RSS feeds or SOAP responses), traditional XML parsers like SimpleXML or DOMDocument can quickly become memory-intensive and slow.

That’s where the PHP XML Expat parser comes in—a fast, event-driven XML parser built directly into PHP through the xml extension.

The Expat parser processes XML data as it reads, triggering callback functions for start and end elements and character data. This makes it ideal for streaming large XML files or handling XML feeds with minimal memory usage.

In this guide, you’ll learn:

• What Expat is

• How to use it step-by-step

• When and why to prefer it over other parsers

• Real-world code examples

✅ What is PHP XML Expat Parser?

Expat is a stream-based XML parser that reads an XML file from top to bottom and triggers event callbacks when it encounters XML tags or text content.

Think of it like a SAX parser—you define handler functions, and PHP calls them when it hits start tags, end tags, or data.

Setting Up XML Expat in PHP

Before you begin, ensure that the xml extension is enabled in your php.ini (it usually is by default in most PHP installations).

Step-by-Step: Parsing XML with PHP Expat

✅ Step 1: Create a Parser Resource

$parser = xml_parser_create();

✅ Step 2: Define Handler Functions

You must define three types of handlers:

• Start element

• End element

• Character data

function startElement($parser, $name, $attrs) {
    echo "Start element: $name\n";
}

function endElement($parser, $name) {
    echo "End element: $name\n";
}

function characterData($parser, $data) {
    echo "Data: $data\n";
}

✅ Step 3: Attach Handlers to the Parser

xml_set_element_handler($parser, "startElement", "endElement");
xml_set_character_data_handler($parser, "characterData");

✅ Step 4: Load & Parse the XML

$xmlData = file_get_contents("books.xml");

if (!xml_parse($parser, $xmlData, true)) {
    echo "XML Error: " . xml_error_string(xml_get_error_code($parser));
}

xml_parser_free($parser);

Full Working Example: PHP XML Expat in Action

books.xml

<library>
    <book id="101">
        <title>PHP for Beginners</title>
        <author>John Doe</author>
    </book>
    <book id="102">
        <title>Advanced PHP</title>
        <author>Jane Smith</author>
    </book>
</library>

expat_parser.php

<?php
function startElement($parser, $name, $attrs) {
    echo "<strong>Start: $name</strong><br>";
    foreach ($attrs as $key => $value) {
        echo "Attribute - $key: $value<br>";
    }
}

function endElement($parser, $name) {
    echo "<strong>End: $name</strong><br>";
}

function characterData($parser, $data) {
    $data = trim($data);
    if ($data) {
        echo "Content: $data<br>";
    }
}

// 1. Create parser
$parser = xml_parser_create();

// 2. Set handlers
xml_set_element_handler($parser, "startElement", "endElement");
xml_set_character_data_handler($parser, "characterData");

// 3. Read and parse file
$xml = file_get_contents("books.xml");

if (!xml_parse($parser, $xml, true)) {
    echo "XML error: " . xml_error_string(xml_get_error_code($parser));
}

// 4. Free parser
xml_parser_free($parser);
?>

Output:

Start: LIBRARY
Start: BOOK
Attribute - ID: 101
Start: TITLE
Content: PHP for Beginners
End: TITLE
Start: AUTHOR
Content: John Doe
End: AUTHOR
End: BOOK
...

Tips & Common Pitfalls

✅ Tips

• Use trim() in your character handler to remove unwanted whitespace.

• Combine data from multiple calls to characterData() for long text blocks.

• Use global variables or an object to store parsed data, since callbacks are stateless.

❌ Common Pitfalls

• Forgetting to free the parser with xml_parser_free().

• Not handling character data properly—it may be called multiple times for a single text node.

• Assuming elements will appear in a fixed order.

Comparison: Expat vs SimpleXML vs DOM

✅ Conclusion & Best Practices

The PHP XML Expat parser is a powerful tool for parsing XML documents efficiently and flexibly, especially when dealing with large or streamed XML data.

Best Practices Recap

• Use Expat for performance-critical XML parsing tasks.

• Always define clear, modular handler functions.

• Store parsed data in a structured format (e.g., arrays or objects).

• Handle all parsing errors gracefully.