QXmlStreamReader 类

QXmlStreamReader 类为凭借简单流化 API 读取格式良好的 XML 提供快速剖析器。 更多...

头：	#include <QXmlStreamReader>
CMake:	find_package(Qt6 REQUIRED COMPONENTS Core) target_link_libraries(mytarget PRIVATE Qt6::Core)
qmake:	QT += core

• 所有成员列表，包括继承成员
• QXmlStreamReader is part of XML 类 .

注意： 此类的所有函数 可重入 .

公共类型

enum	Error { NoError, CustomError, NotWellFormedError, PrematureEndOfDocumentError, UnexpectedElementError }
enum	ReadElementTextBehaviour { ErrorOnUnexpectedElement, IncludeChildElements, SkipChildElements }
enum	TokenType { NoToken, Invalid, StartDocument, EndDocument, StartElement, …, ProcessingInstruction }

特性

• namespaceProcessing : bool

公共函数

	QXmlStreamReader ()
	QXmlStreamReader (QIODevice * device )
	QXmlStreamReader (const QByteArray & data )
	QXmlStreamReader (QAnyStringView data )
	~QXmlStreamReader ()
void	addData (QAnyStringView data )
void	addData (const QByteArray & data )
void	addExtraNamespaceDeclaration (const QXmlStreamNamespaceDeclaration & extraNamespaceDeclaration )
void	addExtraNamespaceDeclarations (const QXmlStreamNamespaceDeclarations & extraNamespaceDeclarations )
bool	atEnd () const
QXmlStreamAttributes	属性 () const
qint64	characterOffset () const
void	clear ()
qint64	columnNumber () const
QIODevice *	device () const
QStringView	documentEncoding () const
QStringView	documentVersion () const
QStringView	dtdName () const
QStringView	dtdPublicId () const
QStringView	dtdSystemId () const
QXmlStreamEntityDeclarations	entityDeclarations () const
int	entityExpansionLimit () const
QXmlStreamEntityResolver *	entityResolver () const
QXmlStreamReader::Error	error () const
QString	errorString () const
bool	hasError () const
(从 6.6 起) bool	hasStandaloneDeclaration () const
bool	isCDATA () const
bool	isCharacters () const
bool	isComment () const
bool	isDTD () const
bool	isEndDocument () const
bool	isEndElement () const
bool	isEntityReference () const
bool	isProcessingInstruction () const
bool	isStandaloneDocument () const
bool	isStartDocument () const
bool	isStartElement () const
bool	isWhitespace () const
qint64	lineNumber () const
QStringView	name () const
QXmlStreamNamespaceDeclarations	namespaceDeclarations () const
bool	namespaceProcessing () const
QStringView	namespaceUri () const
QXmlStreamNotationDeclarations	notationDeclarations () const
QStringView	prefix () const
QStringView	processingInstructionData () const
QStringView	processingInstructionTarget () const
QStringView	qualifiedName () const
void	raiseError (const QString & message = QString())
QString	readElementText (QXmlStreamReader::ReadElementTextBehaviour behaviour = ErrorOnUnexpectedElement)
QXmlStreamReader::TokenType	readNext ()
bool	readNextStartElement ()
void	setDevice (QIODevice * device )
void	setEntityExpansionLimit (int limit )
void	setEntityResolver (QXmlStreamEntityResolver * resolver )
void	setNamespaceProcessing (bool)
void	skipCurrentElement ()
QStringView	text () const
QString	tokenString () const
QXmlStreamReader::TokenType	tokenType () const

详细描述

QXmlStreamReader 提供剖析格式良好 XML 的简单流 API。它是替代以先将完整 XML 载入 DOM 树 (见 QDomDocument )。 QXmlStreamReader 读取数据从 QIODevice (见 setDevice ())，或从原生 QByteArray (见 addData ()).

Qt 提供 QXmlStreamWriter 为写入 XML。

The basic concept of a stream reader is to report an XML document as a stream of tokens, similar to SAX. The main difference between QXmlStreamReader and SAX is how these XML tokens are reported. With SAX, the application must provide handlers (callback functions) that receive so-called XML events from the parser at the parser's convenience. With QXmlStreamReader, the application code itself drives the loop and pulls tokens from the reader, one after another, as it needs them. This is done by calling readNext (), where the reader reads from the input stream until it completes the next token, at which point it returns the tokenType (). A set of convenient functions including isStartElement () 和 text () can then be used to examine the token to obtain information about what has been read. The big advantage of this pulling approach is the possibility to build recursive descent parsers with it, meaning you can split your XML parsing code easily into different methods or classes. This makes it easy to keep track of the application's own state when parsing XML.

A typical loop with QXmlStreamReader looks like this:

  QXmlStreamReader xml;
  ...
  while (!xml.atEnd()) {
        xml.readNext();
        ... // do processing
  }
  if (xml.hasError()) {
        ... // do error handling
  }
					

QXmlStreamReader is a well-formed XML 1.0 parser that does not include external parsed entities. As long as no error occurs, the application code can thus be assured, that

• the data provided by the stream reader satisfies the W3C's criteria for well-formed XML,
• tokens are provided in a valid order.

Unless QXmlStreamReader raises an error, it guarantees the following:

• All tags are nested and closed properly.
• References to internal entities have been replaced with the correct replacement text.
• Attributes have been normalized or added according to the internal subset of the DTD .
• Tokens of type StartDocument happen before all others, aside from comments and processing instructions.
• At most one DOCTYPE element (a token of type DTD ) is present.
• If present, the DOCTYPE appears before all other elements, aside from StartDocument , comments and processing instructions.

In particular, once any token of type StartElement , EndElement , Characters , EntityReference or EndDocument is seen, no tokens of type StartDocument or DTD will be seen. If one is present in the input stream, out of order, an error is raised.

注意： The token types 注释 and ProcessingInstruction may appear anywhere in the stream.

若剖析时出现错误， atEnd () 和 hasError () 返回 true，和 error () 返回出现的错误。函数 errorString (), lineNumber (), columnNumber ()，和 characterOffset () are for constructing an appropriate error or warning message. To simplify application code, QXmlStreamReader contains a raiseError () mechanism that lets you raise custom errors that trigger the same error handling described.

The QXmlStream 书签范例 illustrates how to use the recursive descent technique to read an XML bookmark file (XBEL) with a stream reader.

名称空间

QXmlStream understands and resolves XML namespaces. E.g. in case of a StartElement , namespaceUri () returns the namespace the element is in, and name () returns the element's local name. The combination of namespaceUri and name uniquely identifies an element. If a namespace prefix was not declared in the XML entities parsed by the reader, the namespaceUri is empty.

If you parse XML data that does not utilize namespaces according to the XML specification or doesn't use namespaces at all, you can use the element's qualifiedName () instead. A qualified name is the element's prefix () followed by colon followed by the element's local name () - exactly like the element appears in the raw XML data. Since the mapping namespaceUri to prefix is neither unique nor universal, qualifiedName () should be avoided for namespace-compliant XML data.

In order to parse standalone documents that do use undeclared namespace prefixes, you can turn off namespace processing completely with the namespaceProcessing 特性。

增量剖析

QXmlStreamReader is an incremental parser. It can handle the case where the document can't be parsed all at once because it arrives in chunks (e.g. from multiple files, or over a network connection). When the reader runs out of data before the complete document has been parsed, it reports a PrematureEndOfDocumentError . When more data arrives, either because of a call to addData () or because more data is available through the network device (), the reader recovers from the PrematureEndOfDocumentError error and continues parsing the new data with the next call to readNext ().

For example, if your application reads data from the network using a network access manager , you would issue a network request to the manager and receive a network reply in return. Since a QNetworkReply 是 QIODevice , you connect its readyRead () signal to a custom slot, e.g. slotReadyRead() in the code snippet shown in the discussion for QNetworkAccessManager . In this slot, you read all available data with readAll () and pass it to the XML stream reader using addData (). Then you call your custom parsing function that reads the XML events from the reader.

性能和内存消耗

QXmlStreamReader is memory-conservative by design, since it doesn't store the entire XML document tree in memory, but only the current token at the time it is reported. In addition, QXmlStreamReader avoids the many small string allocations that it normally takes to map an XML document to a convenient and Qt-ish API. It does this by reporting all string data as QStringView rather than real QString objects. Calling toString () on any of those objects returns an equivalent real QString 对象。

成员类型文档编制

enum QXmlStreamReader:: Error

此枚举指定不同错误情况

常量	值	描述
QXmlStreamReader::NoError	0	没有出现错误。
QXmlStreamReader::CustomError	2	引发自定义错误采有 raiseError ()
QXmlStreamReader::NotWellFormedError	3	The parser internally raised an error due to the read XML not being well-formed.
QXmlStreamReader::PrematureEndOfDocumentError	4	The input stream ended before a well-formed XML document was parsed. Recovery from this error is possible if more XML arrives in the stream, either by calling addData () or by waiting for it to arrive on the device ().
QXmlStreamReader::UnexpectedElementError	1	The parser encountered an element or token that was different to those it expected.

enum QXmlStreamReader:: ReadElementTextBehaviour

此枚举指定不同行为在 readElementText ().

常量	值	描述
QXmlStreamReader::ErrorOnUnexpectedElement	0	Raise an UnexpectedElementError and return what was read so far when a child element is encountered.
QXmlStreamReader::IncludeChildElements	1	Recursively include the text from child elements.
QXmlStreamReader::SkipChildElements	2	跳过子级元素。

enum QXmlStreamReader:: TokenType

此枚举指定读取器刚刚读取的令牌类型。

常量	值	描述
QXmlStreamReader::NoToken	0	读取器尚未读取任何内容。
QXmlStreamReader::Invalid	1	发生错误，报告在 error () 和 errorString ().
QXmlStreamReader::StartDocument	2	The reader reports the XML version number in documentVersion (), and the encoding as specified in the XML document in documentEncoding (). If the document is declared standalone, isStandaloneDocument () 返回 true ；否则，返回 false .
QXmlStreamReader::EndDocument	3	The reader reports the end of the document.
QXmlStreamReader::StartElement	4	The reader reports the start of an element with namespaceUri () 和 name (). Empty elements are also reported as StartElement, followed directly by EndElement. The convenience function readElementText () can be called to concatenate all content until the corresponding EndElement. Attributes are reported in 属性 (), namespace declarations in namespaceDeclarations ().
QXmlStreamReader::EndElement	5	The reader reports the end of an element with namespaceUri () 和 name ().
QXmlStreamReader::Characters	6	The reader reports characters in text (). If the characters are all white-space, isWhitespace () 返回 true . If the characters stem from a CDATA section, isCDATA () 返回 true .
QXmlStreamReader::Comment	7	读取器报告注释按 text ().
QXmlStreamReader::DTD	8	The reader reports a DTD in text (), notation declarations in notationDeclarations (), and entity declarations in entityDeclarations (). Details of the DTD declaration are reported in dtdName (), dtdPublicId ()，和 dtdSystemId ().
QXmlStreamReader::EntityReference	9	The reader reports an entity reference that could not be resolved. The name of the reference is reported in name (), the replacement text in text ().
QXmlStreamReader::ProcessingInstruction	10	The reader reports a processing instruction in processingInstructionTarget () 和 processingInstructionData ().

特性文档编制

namespaceProcessing : bool

This property holds the namespace-processing flag of the stream reader.

此特性控制流读取器是否处理名称空间。若启用，读取器处理名称空间，否则不。

默认情况下，名称空间处理是启用的。

访问函数：

bool	namespaceProcessing () const
void	setNamespaceProcessing (bool)

成员函数文档编制

QXmlStreamReader:: QXmlStreamReader ()

构造流读取器。

另请参阅 setDevice () 和 addData ().

[explicit] QXmlStreamReader:: QXmlStreamReader ( QIODevice * device )

创建的新流读取器读取自 device .

另请参阅 setDevice () 和 clear ().

[explicit] QXmlStreamReader:: QXmlStreamReader (const QByteArray & data )

这是重载函数。

创建的新流读取器读取自 data .

另请参阅 addData (), clear ()，和 setDevice ().

[explicit] QXmlStreamReader:: QXmlStreamReader ( QAnyStringView data )

创建的新流读取器读取自 data .

注意： In Qt versions prior to 6.5, this constructor was overloaded for QString and const char* .

另请参阅 addData (), clear ()，和 setDevice ().

[noexcept] QXmlStreamReader:: ~QXmlStreamReader ()

销毁读取器。

void QXmlStreamReader:: addData ( QAnyStringView data )

添加更多 data for the reader to read. This function does nothing if the reader has a device ().

注意： In Qt versions prior to 6.5, this function was overloaded for QString and const char* .

另请参阅 readNext () 和 clear ().

void QXmlStreamReader:: addData (const QByteArray & data )

这是重载函数。

添加更多 data for the reader to read. This function does nothing if the reader has a device ().

另请参阅 readNext () 和 clear ().

void QXmlStreamReader:: addExtraNamespaceDeclaration (const QXmlStreamNamespaceDeclaration & extraNamespaceDeclaration )

添加 extraNamespaceDeclaration . The declaration will be valid for children of the current element, or - should the function be called before any elements are read - for the entire XML document.

另请参阅 namespaceDeclarations (), addExtraNamespaceDeclarations ()，和 setNamespaceProcessing ().

void QXmlStreamReader:: addExtraNamespaceDeclarations (const QXmlStreamNamespaceDeclarations & extraNamespaceDeclarations )

Adds a vector of declarations specified by extraNamespaceDeclarations .

另请参阅 namespaceDeclarations () 和 addExtraNamespaceDeclaration ().

bool QXmlStreamReader:: atEnd () const

返回 true if the reader has read until the end of the XML document, or if an error () has occurred and reading has been aborted. Otherwise, it returns false .

当 atEnd() 和 hasError () 返回 true 且 error () 返回 PrematureEndOfDocumentError , it means the XML has been well-formed so far, but a complete XML document has not been parsed. The next chunk of XML can be added with addData (), if the XML is being read from a QByteArray , or by waiting for more data to arrive if the XML is being read from a QIODevice . Either way, atEnd() will return false once more data is available.

另请参阅 hasError (), error (), device ()，和 QIODevice::atEnd ().

QXmlStreamAttributes QXmlStreamReader:: 属性 () const

返回属性为 StartElement .

qint64 QXmlStreamReader:: characterOffset () const

返回当前字符偏移，从 0 开始。

另请参阅 lineNumber () 和 columnNumber ().

void QXmlStreamReader:: clear ()

移除任何 device () or data from the reader and resets its internal state to the initial state.

另请参阅 addData ().

qint64 QXmlStreamReader:: columnNumber () const

返回当前列号，从 0 开始。

另请参阅 lineNumber () 和 characterOffset ().

QIODevice *QXmlStreamReader:: device () const

返回被当前设备关联的 QXmlStreamReader ，或 nullptr 若没有设备被赋值。

另请参阅 setDevice ().

QStringView QXmlStreamReader:: documentEncoding () const

若 tokenType () 是 StartDocument , this function returns the encoding string as specified in the XML declaration. Otherwise an empty string is returned.

QStringView QXmlStreamReader:: documentVersion () const

若 tokenType () 是 StartDocument , this function returns the version string as specified in the XML declaration. Otherwise an empty string is returned.

QStringView QXmlStreamReader:: dtdName () const

若 tokenType () 是 DTD ，此函数返回 DTD 名称。否则返回空字符串。

QStringView QXmlStreamReader:: dtdPublicId () const

若 tokenType () 是 DTD , this function returns the DTD's public identifier. Otherwise an empty string is returned.

QStringView QXmlStreamReader:: dtdSystemId () const

若 tokenType () 是 DTD , this function returns the DTD's system identifier. Otherwise an empty string is returned.

QXmlStreamEntityDeclarations QXmlStreamReader:: entityDeclarations () const

若 tokenType () 是 DTD , this function returns the DTD's unparsed (external) entity declarations. Otherwise an empty vector is returned.

The QXmlStreamEntityDeclarations class is defined to be a QList of QXmlStreamEntityDeclaration .

int QXmlStreamReader:: entityExpansionLimit () const

Returns the maximum amount of characters a single entity is allowed to expand into. If a single entity expands past the given limit, the document is not considered well formed.

另请参阅 setEntityExpansionLimit .

QXmlStreamEntityResolver *QXmlStreamReader:: entityResolver () const

返回实体解析器，或 nullptr 若没有实体解析器。

另请参阅 setEntityResolver ().

QXmlStreamReader::Error QXmlStreamReader:: error () const

返回当前错误的类型，或 NoError 若没有出现错误。

另请参阅 errorString () 和 raiseError ().

QString QXmlStreamReader:: errorString () const

返回错误消息，设置采用 raiseError ().

另请参阅 error (), lineNumber (), columnNumber ()，和 characterOffset ().

bool QXmlStreamReader:: hasError () const

返回 true 若有发生错误，否则 false .

另请参阅 errorString () 和 error ().

[since 6.6] bool QXmlStreamReader:: hasStandaloneDeclaration () const

返回 true if this document has an explicit standalone declaration (can be 'yes' or 'no'); otherwise returns false ;

若未剖析 XML 声明，此函数返回 false .

该函数在 Qt 6.6 引入。

另请参阅 isStandaloneDocument ().

bool QXmlStreamReader:: isCDATA () const

返回 true 若读取器报告源自 CDATA 区间的字符；否则返回 false .

另请参阅 isCharacters () 和 text ().

bool QXmlStreamReader:: isCharacters () const

返回 true if tokenType () 等于 Characters ；否则返回 false .

另请参阅 isWhitespace () 和 isCDATA ().

bool QXmlStreamReader:: isComment () const

返回 true if tokenType () 等于 注释 ；否则返回 false .

bool QXmlStreamReader:: isDTD () const

返回 true if tokenType () 等于 DTD ；否则返回 false .

bool QXmlStreamReader:: isEndDocument () const

返回 true if tokenType () 等于 EndDocument ；否则返回 false .

bool QXmlStreamReader:: isEndElement () const

返回 true if tokenType () 等于 EndElement ；否则返回 false .

bool QXmlStreamReader:: isEntityReference () const

返回 true if tokenType () 等于 EntityReference ；否则返回 false .

bool QXmlStreamReader:: isProcessingInstruction () const

返回 true if tokenType () 等于 ProcessingInstruction ；否则返回 false .

bool QXmlStreamReader:: isStandaloneDocument () const

返回 true if this document has been declared standalone in the XML declaration; otherwise returns false .

若未剖析 XML 声明，此函数返回 false .

另请参阅 hasStandaloneDeclaration ().

bool QXmlStreamReader:: isStartDocument () const

返回 true if tokenType () 等于 StartDocument ；否则返回 false .

bool QXmlStreamReader:: isStartElement () const

返回 true if tokenType () 等于 StartElement ；否则返回 false .

bool QXmlStreamReader:: isWhitespace () const

返回 true if the reader reports characters that only consist of white-space; otherwise returns false .

另请参阅 isCharacters () 和 text ().

qint64 QXmlStreamReader:: lineNumber () const

返回当前行号，从 1 开始。

另请参阅 columnNumber () 和 characterOffset ().

QStringView QXmlStreamReader:: name () const

返回本地名称为 StartElement , EndElement ，或 EntityReference .

另请参阅 namespaceUri () 和 qualifiedName ().

QXmlStreamNamespaceDeclarations QXmlStreamReader:: namespaceDeclarations () const

若 tokenType () 是 StartElement , this function returns the element's namespace declarations. Otherwise an empty vector is returned.

The QXmlStreamNamespaceDeclarations class is defined to be a QList of QXmlStreamNamespaceDeclaration .

另请参阅 addExtraNamespaceDeclaration () 和 addExtraNamespaceDeclarations ().

QStringView QXmlStreamReader:: namespaceUri () const

返回 namespaceUri 为 StartElement or EndElement .

另请参阅 name () 和 qualifiedName ().

QXmlStreamNotationDeclarations QXmlStreamReader:: notationDeclarations () const

若 tokenType () 是 DTD , this function returns the DTD's notation declarations. Otherwise an empty vector is returned.

The QXmlStreamNotationDeclarations class is defined to be a QList of QXmlStreamNotationDeclaration .

QStringView QXmlStreamReader:: prefix () const

返回前缀为 StartElement or EndElement .

另请参阅 name () 和 qualifiedName ().

QStringView QXmlStreamReader:: processingInstructionData () const

返回数据为 ProcessingInstruction .

QStringView QXmlStreamReader:: processingInstructionTarget () const

Returns the target of a ProcessingInstruction .

QStringView QXmlStreamReader:: qualifiedName () const

Returns the qualified name of a StartElement or EndElement ;

A qualified name is the raw name of an element in the XML data. It consists of the namespace prefix, followed by colon, followed by the element's local name. Since the namespace prefix is not unique (the same prefix can point to different namespaces and different prefixes can point to the same namespace), you shouldn't use qualifiedName(), but the resolved namespaceUri () and the attribute's local name ().

另请参阅 name (), prefix ()，和 namespaceUri ().

void QXmlStreamReader:: raiseError (const QString & message = QString())

引发自定义错误采用可选错误 message .

另请参阅 error () 和 errorString ().

QString QXmlStreamReader:: readElementText ( QXmlStreamReader::ReadElementTextBehaviour behaviour = ErrorOnUnexpectedElement)

Convenience function to be called in case a StartElement was read. Reads until the corresponding EndElement and returns all text in-between. In case of no error, the current token (see tokenType ()) after having called this function is EndElement .

函数串联 text () 当它读取 Characters or EntityReference 令牌，但跳过 ProcessingInstruction and 注释 . If the current token is not StartElement , an empty string is returned.

The behaviour defines what happens in case anything else is read before reaching EndElement . The function can include the text from child elements (useful for example for HTML), ignore child elements, or raise an UnexpectedElementError and return what was read so far (default).

QXmlStreamReader::TokenType QXmlStreamReader:: readNext ()

读取下一令牌并返回其类型。

With one exception, once an error () is reported by readNext(), further reading of the XML stream is not possible. Then atEnd () 返回 true , hasError () 返回 true , and this function returns QXmlStreamReader::Invalid .

The exception is when error () 返回 PrematureEndOfDocumentError . This error is reported when the end of an otherwise well-formed chunk of XML is reached, but the chunk doesn't represent a complete XML document. In that case, parsing can be resumed by calling addData () to add the next chunk of XML, when the stream is being read from a QByteArray , or by waiting for more data to arrive when the stream is being read from a device ().

另请参阅 tokenType () 和 tokenString ().

bool QXmlStreamReader:: readNextStartElement ()

Reads until the next start element within the current element. Returns true when a start element was reached. When the end element was reached, or when an error occurred, false is returned.

The current element is the element matching the most recently parsed start element of which a matching end element has not yet been reached. When the parser has reached the end element, the current element becomes the parent element.

This is a convenience function for when you're only concerned with parsing XML elements. The QXmlStream 书签范例 makes extensive use of this function.

另请参阅 readNext ().

void QXmlStreamReader:: setDevice ( QIODevice * device )

把当前设备设为 device 。设置设备将流重置到其初始状态。

另请参阅 device () 和 clear ().

void QXmlStreamReader:: setEntityExpansionLimit ( int limit )

Sets the maximum amount of characters a single entity is allowed to expand into to limit . If a single entity expands past the given limit, the document is not considered well formed.

The limit is there to prevent DoS attacks when loading unknown XML documents where recursive entity expansion could otherwise exhaust all available memory.

此特性的默认值为 4096 字符。

另请参阅 entityExpansionLimit .

void QXmlStreamReader:: setEntityResolver ( QXmlStreamEntityResolver * resolver )

使 resolver the new entityResolver ().

The stream reader does not take ownership of the resolver. It's the callers responsibility to ensure that the resolver is valid during the entire life-time of the stream reader object, or until another resolver or nullptr 有设置。

另请参阅 entityResolver ().

void QXmlStreamReader:: skipCurrentElement ()

Reads until the end of the current element, skipping any child nodes. This function is useful for skipping unknown elements.

The current element is the element matching the most recently parsed start element of which a matching end element has not yet been reached. When the parser has reached the end element, the current element becomes the parent element.

QStringView QXmlStreamReader:: text () const

Returns the text of Characters , 注释 , DTD ，或 EntityReference .

QString QXmlStreamReader:: tokenString () const

以字符串形式返回读取器的当前令牌。

另请参阅 tokenType ().

QXmlStreamReader::TokenType QXmlStreamReader:: tokenType () const

返回当前令牌类型。

当前令牌也可以查询采用方便函数 isStartDocument (), isEndDocument (), isStartElement (), isEndElement (), isCharacters (), isComment (), isDTD (), isEntityReference ()，和 isProcessingInstruction ().

另请参阅 tokenString ().

内容

• 公共类型

• 特性

• 公共函数

• 详细描述

• 名称空间

• 增量剖析

• 性能和内存消耗