XML operation of PHP extension (2) - XML ​​parser installation and overview

1. Overview and installation

XML (eXtensible Markup Language) is a language used on the Internet. A data format for interacting with structured documents. It is a standard defined by the Internet Society (W3C). Information about XML and related technologies can be found at //m.sbmmt.com/.

This PHP extension implementation supports expat written in PHP by James Clark. This toolkit can parse (but not validate) XML documents. It supports 3 character encodings provided by PHP: US-ASCII, ISO-8859-1 and UTF-8. UTF-16 is not supported.

This extension creates an XML parser and defines handlers for different XML events. Each XML parser also has a handful of parameters that can be adjusted.

This extension requires the libxml PHP extension. This means that --enable-libxml needs to be used, although this will be done implicitly since libxml is enabled by default.

By default, this extension uses expat compat layer. You can also use expat. This library is located at //m.sbmmt.com/. Using the Makefile in the expat library will not build the library file by default. You can use the following build rules to build:

libexpat.a: $(OBJS)
    ar -rc $@ $(OBJS)
    ranlib $@

--disable-xml

--disable-xml. If you compile PHP as a module with Apache 1.3.9 or higher, PHP will automatically use the expat library bundled with Apache. If you do not want to use the bundled expat library, please use the parameter --with-expat-dir=DIR when running PHP's configure configuration script, where DIR should point to the root directory of the expat installation.

3. Capitalization conversion

The element processing function can convert the element name into case-folded (capital letters) form. Case-folding is defined as "a string operation that replaces non-uppercase letters with their corresponding uppercase letters." In other words, in XML, case-folding is converting to uppercase.

By default, all element names passed through the processing function are converted to uppercase letters. Each XML parser can query and control this function through the xml_parser_get_option() and xml_parser_set_option() functions respectively.

4. Error codes

The following constants are XML-related error codes (return values ​​of the xml_parse() function):

• XML_ERROR_NONE

• XML_ERROR_NO_MEMORY

• XML_ERROR_SYNTAX

• XML_ERROR_NO_ELEMENTS

• XML_ERROR_INVALID_TOKEN

• XML_ERROR_UNCLOSED_TOKEN

• XML_ERROR_PARTIAL_CHAR

• XML_ERROR_TAG_MISMATCH

• XML_ERROR_DUPLICATE_ATTRIBUTE

• ##XML_ERROR_JUNK_AFTER_DOC_ELEMENT

##XML_ERROR_PARAM_ENTITY_REF
##XML_ERROR_RECURSIVE_ENTITY_REF
XML_ERROR_ASYNC_ENTITY
XML_ERROR_BAD_CHAR_REF
• #XML_ERROR_ATTRIBUTE_EXTERNAL_ENTITY_REF

##XML_ERROR_MISPLACED_XML_PI

• ##XML_ERROR_UNKNOWN_ENCODING

• XML_ERROR_INCORRECT_ENCODING

• XML_ERROR_UNCLOSED_CDATA_SECTION

• XML_ERROR_EXTERNAL_ENTITY_HANDLING

• ##5. Character encoding

PHP’s XML extension passes through several different The character encoding supports the Unicode character set. There are two types of character encodings, original encoding and target encoding. In PHP's internal presentation, documents are always encoded in UTF-8.

• When the XML is parsed, the original encoding is completed. When creating an XML parser, you can specify the original encoding (this encoding cannot be modified later in the XML parser's life cycle). The supported raw encodings are ISO-8859-1, US-ASCII and UTF-8. The first two are single-byte encodings, that is, each character is represented as one byte. UTF-8 can encode characters into a series of variable numbers (up to 21) of bits, arranged into 1 to 4 bytes. The default raw encoding used in PHP is ISO-8859-1.

When PHP passes the data to the XML processing function, the target encoding is completed. When creating an XML processor, the target encoding is set to be the same as the original encoding, but can be modified at will. Target encoding affects character data and tag names, as well as processing instruction targets.

• If the XML parser encounters a character outside the range that the original encoding can represent, it will return an error.

If PHP encounters a character in the parsed XML document that cannot be represented by the specified target encoding, the problem character will be "downgraded". Typically, those characters are replaced with question marks (?).

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