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QDomNode Class Reference
[QtXml module]

The QDomNode class is the base class for all the nodes in a DOM tree. More...

 #include <QDomNode>

This class is not part of the Qt GUI Framework Edition.

Inherited by QDomAttr, QDomCharacterData, QDomDocument, QDomDocumentFragment, QDomDocumentType, QDomElement, QDomEntity, QDomEntityReference, QDomNotation, and QDomProcessingInstruction.

Note: All functions in this class are reentrant.

• List of all members, including inherited members

Public Types

Public Functions

Related Non-Members

Detailed Description

The QDomNode class is the base class for all the nodes in a DOM tree.

Many functions in the DOM return a QDomNode.

You can find out the type of a node using isAttr(), isCDATASection(), isDocumentFragment(), isDocument(), isDocumentType(), isElement(), isEntityReference(), isText(), isEntity(), isNotation(), isProcessingInstruction(), isCharacterData() and isComment().

A QDomNode can be converted into one of its subclasses using toAttr(), toCDATASection(), toDocumentFragment(), toDocument(), toDocumentType(), toElement(), toEntityReference(), toText(), toEntity(), toNotation(), toProcessingInstruction(), toCharacterData() or toComment(). You can convert a node to a null node with clear().

Copies of the QDomNode class share their data using explicit sharing. This means that modifying one node will change all copies. This is especially useful in combination with functions which return a QDomNode, e.g. firstChild(). You can make an independent (deep) copy of the node with cloneNode().

A QDomNode can be null, much like a null pointer. Creating a copy of a null node results in another null node. It is not possible to modify a null node, but it is possible to assign another, possibly non-null node to it. In this case, the copy of the null node will remain null. You can check if a QDomNode is null by calling isNull(). The empty constructor of a QDomNode (or any of the derived classes) creates a null node.

Nodes are inserted with insertBefore(), insertAfter() or appendChild(). You can replace one node with another using replaceChild() and remove a node with removeChild().

To traverse nodes use firstChild() to get a node's first child (if any), and nextSibling() to traverse. QDomNode also provides lastChild(), previousSibling() and parentNode(). To find the first child node with a particular node name use namedItem().

To find out if a node has children use hasChildNodes() and to get a list of all of a node's children use childNodes().

The node's name and value (the meaning of which varies depending on its type) is returned by nodeName() and nodeValue() respectively. The node's type is returned by nodeType(). The node's value can be set with setNodeValue().

The document to which the node belongs is returned by ownerDocument().

Adjacent QDomText nodes can be merged into a single node with normalize().

QDomElement nodes have attributes which can be retrieved with attributes().

QDomElement and QDomAttr nodes can have namespaces which can be retrieved with namespaceURI(). Their local name is retrieved with localName(), and their prefix with prefix(). The prefix can be set with setPrefix().

You can write the XML representation of the node to a text stream with save().

The following example looks for the first element in an XML document and prints the names of all the elements that are its direct children.

 QDomDocument d;
 d.setContent(someXML);
 QDomNode n = d.firstChild();
 while (!n.isNull()) {
     if (n.isElement()) {
         QDomElement e = n.toElement();
         cout << "Element name: " << e.tagName() << endl;
         break;
     }
     n = n.nextSibling();
 }

For further information about the Document Object Model see Level 1 and Level 2 Core. For a more general introduction of the DOM implementation see the QDomDocument documentation.

Member Type Documentation

enum QDomNode::EncodingPolicy

This enum specifies how QDomNode::save() determines what encoding to use when serializing.

See also the overload of the save() function that takes an EncodingPolicy.

This enum was introduced in Qt 4.3.

enum QDomNode::NodeType

This enum defines the type of the node:

Member Function Documentation

QDomNode::QDomNode ()

Constructs a null node.

QDomNode::QDomNode ( const QDomNode & n )

Constructs a copy of n.

The data of the copy is shared (shallow copy): modifying one node will also change the other. If you want to make a deep copy, use cloneNode().

QDomNode::~QDomNode ()

Destroys the object and frees its resources.

QDomNode QDomNode::appendChild ( const QDomNode & newChild )

Appends newChild as the node's last child.

If newChild is the child of another node, it is reparented to this node. If newChild is a child of this node, then its position in the list of children is changed.

If newChild is a QDomDocumentFragment, then the children of the fragment are removed from the fragment and appended.

If newChild is a QDomElement and this node is a QDomDocument that already has an element node as a child, newChild is not added as a child and a null node is returned.

Calling this function on a null node(created, for example, with the default constructor) does nothing.

The DOM specification disallow inserting attribute nodes, but due to historical reasons QDom accept them nevertheless.

See also insertBefore(), insertAfter(), replaceChild(), and removeChild().

QDomNamedNodeMap QDomNode::attributes () const

Returns a named node map of all attributes. Attributes are only provided for QDomElements.

Changing the attributes in the map will also change the attributes of this QDomNode.

QDomNodeList QDomNode::childNodes () const

Returns a list of all direct child nodes.

Most often you will call this function on a QDomElement object.

For example, if the XML document looks like this:

 <body>
 <h1>Heading</h1>
 <p>Hello <b>you</b></p>
 </body>

Then the list of child nodes for the "body"-element will contain the node created by the <h1> tag and the node created by the <p> tag.

The nodes in the list are not copied; so changing the nodes in the list will also change the children of this node.

See also firstChild() and lastChild().

void QDomNode::clear ()

Converts the node into a null node; if it was not a null node before, its type and contents are deleted.

See also isNull().

QDomNode QDomNode::cloneNode ( bool deep = true ) const

Creates a deep (not shallow) copy of the QDomNode.

If deep is true, then the cloning is done recursively which means that all the node's children are deep copied too. If deep is false only the node itself is copied and the copy will have no child nodes.

int QDomNode::columnNumber () const

For nodes created by QDomDocument::setContent(), this function returns the column number in the XML document where the node was parsed. Otherwise, -1 is returned.

This function was introduced in Qt 4.1.

See also lineNumber() and QDomDocument::setContent().

QDomNode QDomNode::firstChild () const

Returns the first child of the node. If there is no child node, a null node is returned. Changing the returned node will also change the node in the document tree.

See also lastChild() and childNodes().

QDomElement QDomNode::firstChildElement ( const QString & tagName = QString() ) const

Returns the first child element with tag name tagName if tagName is non-empty; otherwise returns the first child element. Returns a null element if no such child exists.

See also lastChildElement(), previousSiblingElement(), and nextSiblingElement().

bool QDomNode::hasAttributes () const

Returns true if the node has attributes; otherwise returns false.

See also attributes().

bool QDomNode::hasChildNodes () const

Returns true if the node has one or more children; otherwise returns false.

QDomNode QDomNode::insertAfter ( const QDomNode & newChild, const QDomNode & refChild )

Inserts the node newChild after the child node refChild. refChild must be a direct child of this node. If refChild is null then newChild is appended as this node's last child.

If newChild is the child of another node, it is reparented to this node. If newChild is a child of this node, then its position in the list of children is changed.

If newChild is a QDomDocumentFragment, then the children of the fragment are removed from the fragment and inserted after refChild.

Returns a new reference to newChild on success or a null node on failure.

The DOM specification disallow inserting attribute nodes, but due to historical reasons QDom accept them nevertheless.

See also insertBefore(), replaceChild(), removeChild(), and appendChild().

QDomNode QDomNode::insertBefore ( const QDomNode & newChild, const QDomNode & refChild )

Inserts the node newChild before the child node refChild. refChild must be a direct child of this node. If refChild is null then newChild is inserted as the node's first child.

If newChild is the child of another node, it is reparented to this node. If newChild is a child of this node, then its position in the list of children is changed.

If newChild is a QDomDocumentFragment, then the children of the fragment are removed from the fragment and inserted before refChild.

Returns a new reference to newChild on success or a null node on failure.

The DOM specification disallow inserting attribute nodes, but due to historical reasons QDom accept them nevertheless.

See also insertAfter(), replaceChild(), removeChild(), and appendChild().

bool QDomNode::isAttr () const

Returns true if the node is an attribute; otherwise returns false.

If this function returns true, it does not imply that this object is a QDomAttribute; you can get the QDomAttribute with toAttribute().

See also toAttr().

bool QDomNode::isCDATASection () const

Returns true if the node is a CDATA section; otherwise returns false.

If this function returns true, it does not imply that this object is a QDomCDATASection; you can get the QDomCDATASection with toCDATASection().

See also toCDATASection().

bool QDomNode::isCharacterData () const

Returns true if the node is a character data node; otherwise returns false.

If this function returns true, it does not imply that this object is a QDomCharacterData; you can get the QDomCharacterData with toCharacterData().

See also toCharacterData().

bool QDomNode::isComment () const

Returns true if the node is a comment; otherwise returns false.

If this function returns true, it does not imply that this object is a QDomComment; you can get the QDomComment with toComment().

See also toComment().

bool QDomNode::isDocument () const

Returns true if the node is a document; otherwise returns false.

If this function returns true, it does not imply that this object is a QDomDocument; you can get the QDomDocument with toDocument().

See also toDocument().

bool QDomNode::isDocumentFragment () const

Returns true if the node is a document fragment; otherwise returns false.

If this function returns true, it does not imply that this object is a QDomDocumentFragment; you can get the QDomDocumentFragment with toDocumentFragment().

See also toDocumentFragment().

bool QDomNode::isDocumentType () const

Returns true if the node is a document type; otherwise returns false.

If this function returns true, it does not imply that this object is a QDomDocumentType; you can get the QDomDocumentType with toDocumentType().

See also toDocumentType().

bool QDomNode::isElement () const

Returns true if the node is an element; otherwise returns false.

If this function returns true, it does not imply that this object is a QDomElement; you can get the QDomElement with toElement().

See also toElement().

bool QDomNode::isEntity () const

Returns true if the node is an entity; otherwise returns false.

If this function returns true, it does not imply that this object is a QDomEntity; you can get the QDomEntity with toEntity().

See also toEntity().

bool QDomNode::isEntityReference () const

Returns true if the node is an entity reference; otherwise returns false.

If this function returns true, it does not imply that this object is a QDomEntityReference; you can get the QDomEntityReference with toEntityReference().

See also toEntityReference().

bool QDomNode::isNotation () const

Returns true if the node is a notation; otherwise returns false.

If this function returns true, it does not imply that this object is a QDomNotation; you can get the QDomNotation with toNotation().

See also toNotation().

bool QDomNode::isNull () const

Returns true if this node is null (i.e. if it has no type or contents); otherwise returns false.

bool QDomNode::isProcessingInstruction () const

Returns true if the node is a processing instruction; otherwise returns false.

If this function returns true, it does not imply that this object is a QDomProcessingInstruction; you can get the QProcessingInstruction with toProcessingInstruction().

See also toProcessingInstruction().

bool QDomNode::isSupported ( const QString & feature, const QString & version ) const

Returns true if the DOM implementation implements the feature feature and this feature is supported by this node in the version version; otherwise returns false.

See also QDomImplementation::hasFeature().

bool QDomNode::isText () const

Returns true if the node is a text node; otherwise returns false.

If this function returns true, it does not imply that this object is a QDomText; you can get the QDomText with toText().

See also toText().

QDomNode QDomNode::lastChild () const

Returns the last child of the node. If there is no child node, a null node is returned. Changing the returned node will also change the node in the document tree.

See also firstChild() and childNodes().

QDomElement QDomNode::lastChildElement ( const QString & tagName = QString() ) const

Returns the last child element with tag name tagName if tagName is non-empty; otherwise returns the first child element. Returns a null element if no such child exists.

See also firstChildElement(), previousSiblingElement(), and nextSiblingElement().

int QDomNode::lineNumber () const

For nodes created by QDomDocument::setContent(), this function returns the line number in the XML document where the node was parsed. Otherwise, -1 is returned.

This function was introduced in Qt 4.1.

See also columnNumber() and QDomDocument::setContent().

QString QDomNode::localName () const

If the node uses namespaces, this function returns the local name of the node; otherwise it returns an empty string.

Only nodes of type ElementNode or AttributeNode can have namespaces. A namespace must have been specified at creation time; it is not possible to add a namespace afterwards.

QDomDocument::createAttributeNS()

See also prefix(), namespaceURI(), and QDomDocument::createElementNS().

QDomNode QDomNode::namedItem ( const QString & name ) const

Returns the first direct child node for which nodeName() equals name.

If no such direct child exists, a null node is returned.

See also nodeName().

QString QDomNode::namespaceURI () const

Returns the namespace URI of this node or an empty string if the node has no namespace URI.

Only nodes of type ElementNode or AttributeNode can have namespaces. A namespace URI must be specified at creation time and cannot be changed later.

QDomDocument::createAttributeNS()

See also prefix(), localName(), and QDomDocument::createElementNS().

QDomNode QDomNode::nextSibling () const

Returns the next sibling in the document tree. Changing the returned node will also change the node in the document tree.

If you have XML like this:

 <h1>Heading</h1>
 <p>The text...</p>
 <h2>Next heading</h2>

and this QDomNode represents the <p> tag, nextSibling() will return the node representing the <h2> tag.

See also previousSibling().

QDomElement QDomNode::nextSiblingElement ( const QString & tagName = QString() ) const

Returns the next sibilng element with tag name tagName if tagName is non-empty; otherwise returns any next sibling element. Returns a null element if no such sibling exists.

See also firstChildElement(), previousSiblingElement(), and lastChildElement().

QString QDomNode::nodeName () const

Returns the name of the node.

The meaning of the name depends on the subclass:

Note: This function does not take the presence of namespaces into account when processing the names of element and attribute nodes. As a result, the returned name can contain any namespace prefix that may be present. To obtain the node name of an element or attribute, use localName(); to obtain the namespace prefix, use namespaceURI().

See also nodeValue().

NodeType QDomNode::nodeType () const

Returns the type of the node.

See also toAttr(), toCDATASection(), toDocumentFragment(), toDocument(), toDocumentType(), toElement(), toEntityReference(), toText(), toEntity(), toNotation(), toProcessingInstruction(), toCharacterData(), and toComment().

QString QDomNode::nodeValue () const

Returns the value of the node.

The meaning of the value depends on the subclass:

All the other subclasses do not have a node value and will return an empty string.

See also setNodeValue() and nodeName().

void QDomNode::normalize ()

Calling normalize() on an element converts all its children into a standard form. This means that adjacent QDomText objects will be merged into a single text object (QDomCDATASection nodes are not merged).

QDomDocument QDomNode::ownerDocument () const

Returns the document to which this node belongs.

QDomNode QDomNode::parentNode () const

Returns the parent node. If this node has no parent, a null node is returned (i.e. a node for which isNull() returns true).

QString QDomNode::prefix () const

Returns the namespace prefix of the node or an empty string if the node has no namespace prefix.

Only nodes of type ElementNode or AttributeNode can have namespaces. A namespace prefix must be specified at creation time. If a node was created with a namespace prefix, you can change it later with setPrefix().

If you create an element or attribute with QDomDocument::createElement() or QDomDocument::createAttribute(), the prefix will be an empty string. If you use QDomDocument::createElementNS() or QDomDocument::createAttributeNS() instead, the prefix will not be an empty string; but it might be an empty string if the name does not have a prefix.

QDomDocument::createElementNS() QDomDocument::createAttributeNS()

See also setPrefix(), localName(), and namespaceURI().

QDomNode QDomNode::previousSibling () const

Returns the previous sibling in the document tree. Changing the returned node will also change the node in the document tree.

For example, if you have XML like this:

 <h1>Heading</h1>
 <p>The text...</p>
 <h2>Next heading</h2>

and this QDomNode represents the &lt;p&gt; tag, previousSibling() will return the node representing the &lt;h1&gt; tag.

See also nextSibling().

QDomElement QDomNode::previousSiblingElement ( const QString & tagName = QString() ) const

Returns the previous sibilng element with tag name tagName if tagName is non-empty; otherwise returns any previous sibling element. Returns a null element if no such sibling exists.

See also firstChildElement(), nextSiblingElement(), and lastChildElement().

QDomNode QDomNode::removeChild ( const QDomNode & oldChild )

Removes oldChild from the list of children. oldChild must be a direct child of this node.

Returns a new reference to oldChild on success or a null node on failure.

See also insertBefore(), insertAfter(), replaceChild(), and appendChild().

QDomNode QDomNode::replaceChild ( const QDomNode & newChild, const QDomNode & oldChild )

Replaces oldChild with newChild. oldChild must be a direct child of this node.

If newChild is the child of another node, it is reparented to this node. If newChild is a child of this node, then its position in the list of children is changed.

If newChild is a QDomDocumentFragment, then oldChild is replaced by all of the children of the fragment.

Returns a new reference to oldChild on success or a null node an failure.

See also insertBefore(), insertAfter(), removeChild(), and appendChild().

void QDomNode::save ( QTextStream & str, int indent ) const

Writes the XML representation of the node and all its children to the stream str. This function uses indent as the amount of space to indent the node.

If this node is a document node, the encoding of text stream str's encoding is set by treating a processing instruction by name "xml" as an XML declaration, if such a one exists, and otherwise defaults to UTF-8. XML declarations are not processing instructions, but this behavior exists for historical reasons. If this node is not a document node, the text stream's encoding is used.

If the document contains invalid XML characters or characters that cannot be encoded in the given encoding, the result and behavior is undefined.

void QDomNode::save ( QTextStream & str, int indent, EncodingPolicy encodingPolicy ) const

If encodingPolicy is QDomNode::EncodingFromDocument, this function behaves as save(QTextStream &str, int indent).

If encodingPolicy is EncodingFromTextStream and this node is a document node, this function behaves as save(QTextStream &str, int indent) with the exception that the encoding specified in the text stream str is used.

If the document contains invalid XML characters or characters that cannot be encoded in the given encoding, the result and behavior is undefined.

This function was introduced in Qt 4.2.

void QDomNode::setNodeValue ( const QString & v )

Sets the node's value to v.

See also nodeValue().

void QDomNode::setPrefix ( const QString & pre )

If the node has a namespace prefix, this function changes the namespace prefix of the node to pre. Otherwise this function does nothing.

Only nodes of type ElementNode or AttributeNode can have namespaces. A namespace prefix must have be specified at creation time; it is not possible to add a namespace prefix afterwards.

QDomDocument::createElementNS() QDomDocument::createAttributeNS()

See also prefix(), localName(), and namespaceURI().

QDomAttr QDomNode::toAttr () const

Converts a QDomNode into a QDomAttr. If the node is not an attribute, the returned object will be null.

See also isAttr().

QDomCDATASection QDomNode::toCDATASection () const

Converts a QDomNode into a QDomCDATASection. If the node is not a CDATA section, the returned object will be null.

See also isCDATASection().

QDomCharacterData QDomNode::toCharacterData () const

Converts a QDomNode into a QDomCharacterData. If the node is not a character data node the returned object will be null.

See also isCharacterData().

QDomComment QDomNode::toComment () const

Converts a QDomNode into a QDomComment. If the node is not a comment the returned object will be null.

See also isComment().

QDomDocument QDomNode::toDocument () const

Converts a QDomNode into a QDomDocument. If the node is not a document the returned object will be null.

See also isDocument().

QDomDocumentFragment QDomNode::toDocumentFragment () const

Converts a QDomNode into a QDomDocumentFragment. If the node is not a document fragment the returned object will be null.

See also isDocumentFragment().

QDomDocumentType QDomNode::toDocumentType () const

Converts a QDomNode into a QDomDocumentType. If the node is not a document type the returned object will be null.

See also isDocumentType().

QDomElement QDomNode::toElement () const

Converts a QDomNode into a QDomElement. If the node is not an element the returned object will be null.

See also isElement().

QDomEntity QDomNode::toEntity () const

Converts a QDomNode into a QDomEntity. If the node is not an entity the returned object will be null.

See also isEntity().

QDomEntityReference QDomNode::toEntityReference () const

Converts a QDomNode into a QDomEntityReference. If the node is not an entity reference, the returned object will be null.

See also isEntityReference().

QDomNotation QDomNode::toNotation () const

Converts a QDomNode into a QDomNotation. If the node is not a notation the returned object will be null.

See also isNotation().

QDomProcessingInstruction QDomNode::toProcessingInstruction () const

Converts a QDomNode into a QDomProcessingInstruction. If the node is not a processing instruction the returned object will be null.

See also isProcessingInstruction().

QDomText QDomNode::toText () const

Converts a QDomNode into a QDomText. If the node is not a text, the returned object will be null.

See also isText().

bool QDomNode::operator!= ( const QDomNode & n ) const

Returns true if n and this DOM node are not equal; otherwise returns false.

QDomNode & QDomNode::operator= ( const QDomNode & n )

Assigns a copy of n to this DOM node.

The data of the copy is shared (shallow copy): modifying one node will also change the other. If you want to make a deep copy, use cloneNode().

bool QDomNode::operator== ( const QDomNode & n ) const

Returns true if n and this DOM node are equal; otherwise returns false.

Any instance of QDomNode acts as a reference to an underlying data structure in QDomDocument. The test for equality checks if the two references point to the same underlying node. For example:

 QDomDocument document;
 QDomElement element1 = document.documentElement();
 QDomElement element2 = element1;

The two nodes (QDomElement is a QDomNode subclass) both refer to the document's root element, and element1 == element2 will return true. On the other hand:

 QDomElement element3 = document.createElement("MyElement");
 QDomElement element4 = document.createElement("MyElement");

Even though both nodes are empty elements carrying the same name, element3 == element4 will return false because they refer to two different nodes in the underlying data structure.

Related Non-Members

QTextStream & operator<< ( QTextStream & str, const QDomNode & node )

Writes the XML representation of the node node and all its children to the stream str.