PHP XML Expat
PHP XML Expat Parser
XML is a popular semi-structured file format that stores data in a database-like format. In practical applications, some simple and low-security data are often stored in XML file format. The advantage of this is that on the one hand, it can improve reading efficiency by reducing interactive operations with the database, on the other hand, it can effectively utilize the advantages of XML to reduce the difficulty of program writing.
The built-in Expat parser makes it possible to process XML documents in PHP.
What is XML?
XML is the abbreviation of "eXtensible Markup Language" and is a markup language similar to HTML. But unlike HTML, XML is mainly used to describe data and store data, while HTML is mainly used to display data.
XML is used to describe data, and its focus is what the data is. XML files describe the structure of data.
In XML, there are no predefined tags. You must define your own tags.
For example:
<?xml version="1.0"?> <threads> <thread> <title>Welcome </title> <author>Simon </author> <content>Welcome to XML guestbook!! </content> <thread> </threads>
At the top of an XML file, <?xml version="1.0"?> is usually used to identify the beginning of XML data and the XML data uses standard Version Information.
<thread> and <thread> tags mark this as a message. There is a title, author, and content in the message, which completely expresses a message message.
To learn more about XML, visit our XML tutorial.
What is Expat?
To read and update - create and process - an XML document, you need an XML parser.
There are two basic types of XML parsers:
1. Tree-based parser: This parser converts XML documents into a tree structure. It analyzes the entire document and provides access to elements in the tree, such as the Document Object Model (DOM).
2. Event-based parser: Treat XML documents as a series of events. When a specific event occurs, the parser calls a function to handle it.
The Expat parser is an event-based parser.
Event-based parsers focus on the content of XML documents rather than their structure. Because of this, event-based parsers are able to access data faster than tree-based parsers.
Please see the following XML fragment:
<from>Jani</from>
The event-based parser reports the above XML For a sequence of three events:
Start element: from
Start CDATA section, Value: Jani
Close element: from
The XML example above Contains well-formed XML. However, this instance is invalid XML because there is no document type declaration (DTD) associated with it.
However, this makes no difference when using the Expat parser. Expat is a parser that does not check validity and ignores any DTD.
As an event-based, non-validated XML parser, Expat is fast and lightweight, making it ideal for PHP web applications.
Note: The XML document must be well formed, otherwise Expat will generate an error.
Installation
The XML Expat parser function is an integral part of PHP core. No installation is required to use these functions.
XML file
The following XML file will be used in our example:
<?xml version="1.0" encoding="ISO-8859-1"?> <note> <to>Tove</to> <from>Jani</from> <heading>Reminder</heading> <body>Don't forget me this weekend!</body> </note>
Initialize the XML parser
We need to initialize the XML parser in PHP, define handlers for different XML events, and then parse the XML file .
Example
<?php
//初始化XML解析器
$parser=xml_parser_create();
//在元素开始时使用的函数
function start($parser,$element_name,$element_attrs)
{
switch($element_name)
{
case "NOTE":
echo "-- Note --<br>";
break;
case "TO":
echo "To: ";
break;
case "FROM":
echo "From: ";
break;
case "HEADING":
echo "Heading: ";
break;
case "BODY":
echo "Message: ";
}
}
//函数结束时使用的函数
function stop($parser,$element_name)
{
echo "<br>";
}
//查找字符数据时使用的函数
function char($parser,$data)
{
echo $data;
}
//指定元素的处理
xml_set_element_handler($parser,"start","stop");
//指定数据处理程序
xml_set_character_data_handler($parser,"char");
//打开XML文件
$fp=fopen("test.xml","r");
//读取数据
while ($data=fread($fp,4096))
{
xml_parse($parser,$data,feof($fp)) or
die (sprintf("XML Error: %s at line %d",
xml_error_string(xml_get_error_code($parser)),
xml_get_current_line_number($parser)));
}
//释放内存
xml_parser_free($parser);
?>The above code will output:
-- Note --
To: Tove
From: Jani
Heading: Reminder
Message: Don't forget me this weekend!
Working principle:
1. Initialize the XML parser through the xml_parser_create() function
2 . Create functions that match different event handlers
3. Add the xml_set_element_handler() function to define which function to execute when the parser encounters the start and end tags
4. Add xml_set_character_data_handler( ) function to define which function is executed when the parser encounters character data
5. Use the xml_parse() function to parse the file "test.xml"
6. In case there is an error , add the xml_error_string() function to convert XML errors into text descriptions
7. Call the xml_parser_free() function to release the memory allocated to the xml_parser_create() function
More information about the PHP Expat parser
For more information about the PHP Expat function, please visit our PHP XML Parser Reference Manual.
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