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This article focuses on "how to understand PHP XML Expat". Interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn how to understand PHP XML Expat.

The built-in Expat parser makes it possible to process XML documents in PHP.

What is XML?

XML is used to describe data, and its focus is on what the data is. The XML file describes the structure of the data.

In XML, there are no predefined tags. You must define your own label.

What is Expat?

To read and update-create and process-an XML document, you need a XML parser.

There are two basic types of XML parsers:

Tree-based parser: this parser converts an XML document into a tree structure. It analyzes the entire document and provides API to access elements of the tree species, such as the document object Model (DOM).

Event-based parser: treats an XML document as a series of events. When a specific event occurs, the parser calls a function to handle it.

Expat parsers are event-based parsers.

Event-based parsers focus on the contents of XML documents, not their results. Because of this, event-based parsers can access data faster than tree-based parsers.

Look at the following XML snippet:

John

The event-based parser reports the above XML as a series of three events:

Start element: from

Start the CDATA section, value: John

Close element: from

The above XML example contains a well-formed XML. However, this example is invalid XML because there is no document type declaration (DTD) associated with it, and there is no embedded DTD.

However, when using the Expat parser, this makes no difference. Expat is a parser that does not check for validity and ignores any DTD.

As an event-based, non-validating XML parser, Expat is fast and lightweight, and is very suitable for PHP web applications.

Note: the XML document must be well-formed, or Expat will generate errors.

Installation

The XML Expat parser is part of the core of PHP. These functions can be used without installation.

XML file

The following XML file will be used in our example:

GeorgeJohnReminderDon't forget the meeting!

Initialize the XML parser

We initialize the XML parser in PHP, define handlers for different XML events, and then parse the XML file.

Examples

The output of the above code:

-- Note--

To: George

From: John

Heading: Reminder

Message: Don't forget the meeting!

Explain how it works:

Initialize the XML parser with the xml_parser_create () function

Create functions that match different event handlers

Add the xml_set_element_handler () function to define which function to execute when the parser encounters the start and end tags

Add the xml_set_character_data_handler () function to define which function to execute when the parser encounters character data

Parse the file "test.xml" through the xml_parse () function

In case of an error, add the xml_error_string () function to convert the XML error into a text description

Call the xml_parser_free () function to free the memory allocated to the xml_parser_create () function

At this point, I believe you have a deeper understanding of "how to understand PHP XML Expat". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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