- Qt 5.15
- Qt Core
- C++ Classes
- QXmlStreamWriter
- Qt 5.15.18 Reference Documentation

# QXmlStreamWriter Class

The QXmlStreamWriter class provides an XML writer with a simple streaming API. More...

Header: | #include <QXmlStreamWriter>
qmake: | QT += core
Since: | Qt 4.3

This class was introduced in Qt 4.3.

- List of all members, including inherited members

Note: All functions in this class are reentrant.

## Properties

- autoFormatting : bool
- autoFormattingIndent : int

## Public Functions

| QXmlStreamWriter(QString *string)
| QXmlStreamWriter(QByteArray *array)
| QXmlStreamWriter(QIODevice *device)
| QXmlStreamWriter()
| ~QXmlStreamWriter()
bool | autoFormatting() const
int | autoFormattingIndent() const
QTextCodec * | codec() const
QIODevice * | device() const
bool | hasError() const
void | setAutoFormatting(bool enable)
void | setAutoFormattingIndent(int spacesOrTabs)
void | setCodec(QTextCodec *codec)
void | setCodec(const char *codecName)
void | setDevice(QIODevice *device)
void | writeAttribute(const QString &namespaceUri, const QString &name, const QString &value)
void | writeAttribute(const QString &qualifiedName, const QString &value)
void | writeAttribute(const QXmlStreamAttribute &attribute)
void | writeAttributes(const QXmlStreamAttributes &attributes)
void | writeCDATA(const QString &text)
void | writeCharacters(const QString &text)
void | writeComment(const QString &text)
void | writeCurrentToken(const QXmlStreamReader &reader)
void | writeDTD(const QString &dtd)
void | writeDefaultNamespace(const QString &namespaceUri)
void | writeEmptyElement(const QString &namespaceUri, const QString &name)
void | writeEmptyElement(const QString &qualifiedName)
void | writeEndDocument()
void | writeEndElement()
void | writeEntityReference(const QString &name)
void | writeNamespace(const QString &namespaceUri, const QString &prefix = QString())
void | writeProcessingInstruction(const QString &target, const QString &data = QString())
void | writeStartDocument(const QString &version)
void | writeStartDocument()
void | writeStartDocument(const QString &version, bool standalone)
void | writeStartElement(const QString &namespaceUri, const QString &name)
void | writeStartElement(const QString &qualifiedName)
void | writeTextElement(const QString &namespaceUri, const QString &name, const QString &text)
void | writeTextElement(const QString &qualifiedName, const QString &text)

## Detailed Description

QXmlStreamWriter is the counterpart to QXmlStreamReader for writing XML. Like its related class, it operates on a QIODevice specified with setDevice(). The API is simple and straightforward: for every XML token or event you want to write, the writer provides a specialized function.

You start a document with writeStartDocument() and end it with writeEndDocument(). This will implicitly close all remaining open tags.

Element tags are opened with writeStartElement() followed by writeAttribute() or writeAttributes(), element content, and then writeEndElement(). A shorter form writeEmptyElement() can be used to write empty elements, followed by writeAttributes().

Element content consists of either characters, entity references or nested elements. It is written with writeCharacters(), which also takes care of escaping all forbidden characters and character sequences, writeEntityReference(), or subsequent calls to writeStartElement(). A convenience method writeTextElement() can be used for writing terminal elements that contain nothing but text.

The following abridged code snippet shows the basic use of the class to write formatted XML with indentation:

         QXmlStreamWriter stream(&output);
         stream.setAutoFormatting(true);
         stream.writeStartDocument();
         ...
         stream.writeStartElement("bookmark");
         stream.writeAttribute("href", "http://qt-project.org/");
         stream.writeTextElement("title", "Qt Project");
         stream.writeEndElement(); // bookmark
         ...
         stream.writeEndDocument();

QXmlStreamWriter takes care of prefixing namespaces, all you have to do is specify the `namespaceUri` when writing elements or attributes. If you must conform to certain prefixes, you can force the writer to use them by declaring the namespaces manually with either writeNamespace() or writeDefaultNamespace(). Alternatively, you can bypass the stream writer's namespace support and use overloaded methods that take a qualified name instead. The namespace http://www.w3.org/XML/1998/namespace is implicit and mapped to the prefix xml.

The stream writer can automatically format the generated XML data by adding line-breaks and indentation to empty sections between elements, making the XML data more readable for humans and easier to work with for most source code management systems. The feature can be turned on with the autoFormatting property, and customized with the autoFormattingIndent property.

Other functions are writeCDATA(), writeComment(), writeProcessingInstruction(), and writeDTD(). Chaining of XML streams is supported with writeCurrentToken().

By default, QXmlStreamWriter encodes XML in UTF-8. Different encodings can be enforced using setCodec().

If an error occurs while writing to the underlying device, hasError() starts returning true and subsequent writes are ignored.

The QXmlStream Bookmarks Example illustrates how to use a stream writer to write an XML bookmark file (XBEL) that was previously read in by a QXmlStreamReader.

## Property Documentation

### autoFormatting : bool

The auto-formatting flag of the stream writer

This property controls whether or not the stream writer automatically formats the generated XML data. If enabled, the writer automatically adds line-breaks and indentation to empty sections between elements (ignorable whitespace). The main purpose of auto-formatting is to split the data into several lines, and to increase readability for a human reader. The indentation depth can be controlled through the autoFormattingIndent property.

By default, auto-formatting is disabled.

This property was introduced in Qt 4.4.

Access functions:

bool | autoFormatting() const
void | setAutoFormatting(bool enable)

### autoFormattingIndent : int

This property holds the number of spaces or tabs used for indentation when auto-formatting is enabled. Positive numbers indicate spaces, negative numbers tabs.

The default indentation is 4.

This property was introduced in Qt 4.4.

Access functions:

int | autoFormattingIndent() const
void | setAutoFormattingIndent(int spacesOrTabs)

See also autoFormatting.

## Member Function Documentation

### QXmlStreamWriter::QXmlStreamWriter(QString *string)

Constructs a stream writer that writes into string.

Note that when writing to QString, QXmlStreamWriter ignores the codec set with setCodec(). See that function for more information.

### QXmlStreamWriter::QXmlStreamWriter(QByteArray *array)

Constructs a stream writer that writes into array. This is the same as creating an xml writer that operates on a QBuffer device which in turn operates on array.

### QXmlStreamWriter::QXmlStreamWriter(QIODevice *device)

Constructs a stream writer that writes into device;

### QXmlStreamWriter::QXmlStreamWriter()

Constructs a stream writer.

See also setDevice().

### QXmlStreamWriter::~QXmlStreamWriter()

Destructor.

### bool QXmlStreamWriter::autoFormatting() const

Returns `true` if auto formatting is enabled, otherwise `false`.

Note: Getter function for property autoFormatting.

This function was introduced in Qt 4.4.

See also setAutoFormatting().

### QTextCodec *QXmlStreamWriter::codec() const

Returns the codec that is currently assigned to the stream.

See also setCodec().

### QIODevice *QXmlStreamWriter::device() const

Returns the current device associated with the QXmlStreamWriter, or `nullptr` if no device has been assigned.

See also setDevice().

### bool QXmlStreamWriter::hasError() const

Returns `true` if writing failed.

This can happen if the stream failed to write to the underlying device or if the data to be written contained invalid characters.

The error status is never reset. Writes happening after the error occurred may be ignored, even if the error condition is cleared.

### void QXmlStreamWriter::setAutoFormatting(bool enable)

Enables auto formatting if enable is `true`, otherwise disables it.

The default value is `false`.

Note: Setter function for property autoFormatting.

This function was introduced in Qt 4.4.

See also autoFormatting().

### void QXmlStreamWriter::setCodec(QTextCodec *codec)

Sets the codec for this stream to codec. The codec is used for encoding any data that is written. By default, QXmlStreamWriter uses UTF-8.

The encoding information is stored in the initial xml tag which gets written when you call writeStartDocument(). Call this function before calling writeStartDocument().

Note: When writing the XML to a QString, the codec information is ignored and the XML header will not include any encoding information, since all QStrings are UTF-16. If you later convert the QString to an 8-bit format, you must arrange for the encoding information to be transmitted out-of-band.

See also codec().

### void QXmlStreamWriter::setCodec(const char *codecName)

Sets the codec for this stream to the QTextCodec for the encoding specified by codecName. Common values for `codecName` include "ISO 8859-1", "UTF-8", and "UTF-16". If the encoding isn't recognized, nothing happens.

Note: When writing the XML to a QString, the codec information is ignored and the XML header will not include any encoding information, since all QStrings are UTF-16. If you later convert the QString to an 8-bit format, you must arrange for the encoding information to be transmitted out-of-band.

See also QTextCodec::codecForName().

### void QXmlStreamWriter::setDevice(QIODevice *device)

Sets the current device to device. If you want the stream to write into a QByteArray, you can create a QBuffer device.

See also device().

### void QXmlStreamWriter::writeAttribute(const QString &namespaceUri, const QString &name, const QString &value)

Writes an attribute with name and value, prefixed for the specified namespaceUri. If the namespace has not been declared yet, QXmlStreamWriter will generate a namespace declaration for it.

This function can only be called after writeStartElement() before any content is written, or after writeEmptyElement().

### void QXmlStreamWriter::writeAttribute(const QString &qualifiedName, const QString &value)

This is an overloaded function.

Writes an attribute with qualifiedName and value.

This function can only be called after writeStartElement() before any content is written, or after writeEmptyElement().

### void QXmlStreamWriter::writeAttribute(const QXmlStreamAttribute &attribute)

This is an overloaded function.

Writes the attribute.

This function can only be called after writeStartElement() before any content is written, or after writeEmptyElement().

### void QXmlStreamWriter::writeAttributes(const QXmlStreamAttributes &attributes)

Writes the attribute vector attributes. If a namespace referenced in an attribute not been declared yet, QXmlStreamWriter will generate a namespace declaration for it.

This function can only be called after writeStartElement() before any content is written, or after writeEmptyElement().

See also writeAttribute() and writeNamespace().

### void QXmlStreamWriter::writeCDATA(const QString &text)

Writes text as CDATA section. If text contains the forbidden character sequence "]]>", it is split into different CDATA sections.

This function mainly exists for completeness. Normally you should not need use it, because writeCharacters() automatically escapes all non-content characters.

### void QXmlStreamWriter::writeCharacters(const QString &text)

Writes text. The characters "<", "&", and """ are escaped as entity references "&lt;", "&amp;, and "&quot;". To avoid the forbidden sequence "]]>", ">" is also escaped as "&gt;".

See also writeEntityReference().

### void QXmlStreamWriter::writeComment(const QString &text)

Writes text as XML comment, where text must not contain the forbidden sequence "--" or end with "-". Note that XML does not provide any way to escape "-" in a comment.

### void QXmlStreamWriter::writeCurrentToken(const QXmlStreamReader &reader)

Writes the current state of the reader. All possible valid states are supported.

The purpose of this function is to support chained processing of XML data.

See also QXmlStreamReader::tokenType().

### void QXmlStreamWriter::writeDTD(const QString &dtd)

Writes a DTD section. The dtd represents the entire doctypedecl production from the XML 1.0 specification.

### void QXmlStreamWriter::writeDefaultNamespace(const QString &namespaceUri)

Writes a default namespace declaration for namespaceUri.

If writeStartElement() or writeEmptyElement() was called, the declaration applies to the current element; otherwise it applies to the next child element.

Note that the namespaces http://www.w3.org/XML/1998/namespace (bound to xmlns) and http://www.w3.org/2000/xmlns/ (bound to xml) by definition cannot be declared as default.

### void QXmlStreamWriter::writeEmptyElement(const QString &namespaceUri, const QString &name)

Writes an empty element with name, prefixed for the specified namespaceUri. If the namespace has not been declared, QXmlStreamWriter will generate a namespace declaration for it. Subsequent calls to writeAttribute() will add attributes to this element.

See also writeNamespace().

### void QXmlStreamWriter::writeEmptyElement(const QString &qualifiedName)

This is an overloaded function.

Writes an empty element with qualified name qualifiedName. Subsequent calls to writeAttribute() will add attributes to this element.

### void QXmlStreamWriter::writeEndDocument()

Closes all remaining open start elements and writes a newline.

See also writeStartDocument().

### void QXmlStreamWriter::writeEndElement()

Closes the previous start element.

See also writeStartElement().

### void QXmlStreamWriter::writeEntityReference(const QString &name)

Writes the entity reference name to the stream, as "&name;".

### void QXmlStreamWriter::writeNamespace(const QString &namespaceUri, const QString &prefix = QString())

Writes a namespace declaration for namespaceUri with prefix. If prefix is empty, QXmlStreamWriter assigns a unique prefix consisting of the letter 'n' followed by a number.

If writeStartElement() or writeEmptyElement() was called, the declaration applies to the current element; otherwise it applies to the next child element.

Note that the prefix xml is both predefined and reserved for http://www.w3.org/XML/1998/namespace, which in turn cannot be bound to any other prefix. The prefix xmlns and its URI http://www.w3.org/2000/xmlns/ are used for the namespace mechanism itself and thus completely forbidden in declarations.

### void QXmlStreamWriter::writeProcessingInstruction(const QString &target, const QString &data = QString())

Writes an XML processing instruction with target and data, where data must not contain the sequence "?>".

### void QXmlStreamWriter::writeStartDocument(const QString &version)

Writes a document start with the XML version number version.

See also writeEndDocument().

### void QXmlStreamWriter::writeStartDocument()

This is an overloaded function.

Writes a document start with XML version number "1.0". This also writes the encoding information.

This function was introduced in Qt 4.5.

See also writeEndDocument() and setCodec().

### void QXmlStreamWriter::writeStartDocument(const QString &version, bool standalone)

Writes a document start with the XML version number version and a standalone attribute standalone.

This function was introduced in Qt 4.5.

See also writeEndDocument().

### void QXmlStreamWriter::writeStartElement(const QString &namespaceUri, const QString &name)

Writes a start element with name, prefixed for the specified namespaceUri. If the namespace has not been declared yet, QXmlStreamWriter will generate a namespace declaration for it. Subsequent calls to writeAttribute() will add attributes to this element.

See also writeNamespace(), writeEndElement(), and writeEmptyElement().

### void QXmlStreamWriter::writeStartElement(const QString &qualifiedName)

This is an overloaded function.

Writes a start element with qualifiedName. Subsequent calls to writeAttribute() will add attributes to this element.

See also writeEndElement() and writeEmptyElement().

### void QXmlStreamWriter::writeTextElement(const QString &namespaceUri, const QString &name, const QString &text)

Writes a text element with name, prefixed for the specified namespaceUri, and text. If the namespace has not been declared, QXmlStreamWriter will generate a namespace declaration for it.

This is a convenience function equivalent to:

             writeStartElement(namespaceUri, name);
             writeCharacters(text);
             writeEndElement();

### void QXmlStreamWriter::writeTextElement(const QString &qualifiedName, const QString &text)

This is an overloaded function.

Writes a text element with qualifiedName and text.

This is a convenience function equivalent to:

             writeStartElement(qualifiedName);
             writeCharacters(text);
             writeEndElement();