Expat XML Parser is a stream-oriented XML parser written in C. This utility software is the first available open-source XML parser. It has found a place in various open-source software, such as the Apache HTTP Server, Mozilla, PHP, and Python. Expat excels with files that are too large to fit RAM, and where performance and flexibility are crucial. It is a free program that you can copy, distribute, and modify under the MIT/X Consortium license. 

What is Expat XML Parser?

As noted, Expat is a stream-oriented parser. In the app, you register callback—or handler—functions with the parser. Then you start feeding it the document. The parser will then recognize parts of the documents and call the appropriate handler for that part, assuming that you have registered one. The document will then fed to the parser in pieces, so you can start parsing before you have all the documents. With this, you can parse really huge documents that won’t fit into memory. 

Users, especially beginners, will find the app a bit intimidating because of the many kinds of handlers and options that you can set. However, you only need to learn four functions to do 90% of what you will do with it. You can create a new parser object with XML_ParserCreate and set handlers for start and end tags using the XML_SetElementsHandler. To set a handler for text, you can use the XML_SetCharacterDataHandler. Finally, XML_Parse allows you to pass a buffer full of documents to the parser. 

Typically, programs register handler functions for the XML element to start or stop events and character events. Expat provides facilities for sophisticated event handling. Its parsing events resemble the events defined in the Sample API for XML (SAX). However, Expat is not a SAX-compliant parser. Projects incorporating Expat library often build SAX—and possibly DOM parsers—on top of Expat. But while this app is mainly a stream-based, it supports stopping and restarting parsing at arbitrary times. With this, the implementation of a pull parser is relatively easy. 

Helpful parser library

Since released to the market, Expat XMLP Parser has been a helpful tool. It has been the choice of many higher-level projects. It is highly efficient and very robust. It is also well-tested and complies with the standards. It may be a bit overwhelming due to its many handlers and options, but all in all, you won’t go wrong with this app.