class NamespaceSupport

Library: XML
Package: SAX
Header: Poco/SAX/NamespaceSupport.h


Encapsulate Namespace logic for use by SAX drivers. This class encapsulates the logic of Namespace processing: it tracks the declarations currently in force for each context and automatically processes qualified XML 1.0 names into their Namespace parts; it can also be used in reverse for generating XML 1.0 from Namespaces. Namespace support objects are reusable, but the reset method must be invoked between each session.

Member Summary

Member Functions: declarePrefix, getDeclaredPrefixes, getPrefix, getPrefixes, getURI, isMapped, popContext, processName, pushContext, reset, undeclarePrefix

Types Aliases


using PrefixSet = std::set < XMLString >;




Creates a NamespaceSupport object.




Destroys a NamespaceSupport object.

Member Functions


bool declarePrefix(
    const XMLString & prefix,
    const XMLString & namespaceURI

Declare a Namespace prefix. All prefixes must be declared before they are referenced. For example, a SAX driver (parser) would scan an element's attributes in two passes: first for namespace declarations, then a second pass using processName() to interpret prefixes against (potentially redefined) prefixes.

This method declares a prefix in the current Namespace context; the prefix will remain in force until this context is popped, unless it is shadowed in a descendant context.

To declare the default element Namespace, use the empty string as the prefix.

Note that you must not declare a prefix after you've pushed and popped another Namespace context, or treated the declarations phase as complete by processing a prefixed name.

Returns true if the prefix was legal, false otherwise.


void getDeclaredPrefixes(
    PrefixSet & prefixes
) const;

Return an enumeration of all prefixes declared in this context.

The empty (default) prefix will be included in this enumeration; note that this behaviour differs from that of getPrefix() and getPrefixes().


const XMLString & getPrefix(
    const XMLString & namespaceURI
) const;

Return one of the prefixes mapped to a Namespace URI.

If more than one prefix is currently mapped to the same URI, this method will make an arbitrary selection; if you want all of the prefixes, use the getPrefixes() method instead.


void getPrefixes(
    PrefixSet & prefixes
) const;

Return an enumeration of all prefixes whose declarations are active in the current context. This includes declarations from parent contexts that have not been overridden.

Note: if there is a default prefix, it will not be returned in this enumeration; check for the default prefix using the getURI with an argument of "".


void getPrefixes(
    const XMLString & namespaceURI,
    PrefixSet & prefixes
) const;

Return an enumeration of all prefixes for a given URI whose declarations are active in the current context. This includes declarations from parent contexts that have not been overridden.

This method returns prefixes mapped to a specific Namespace URI. The xml: prefix will be included. If you want only one prefix that's mapped to the Namespace URI, and you don't care which one you get, use the getPrefix() method instead.

Note: the empty (default) prefix is never included in this enumeration; to check for the presence of a default Namespace, use the getURI() method with an argument of "".


const XMLString & getURI(
    const XMLString & prefix
) const;

Look up a prefix and get the currently-mapped Namespace URI.

This method looks up the prefix in the current context. Use the empty string ("") for the default Namespace.


bool isMapped(
    const XMLString & namespaceURI
) const;

Returns true if the given namespaceURI has been mapped to a prefix, false otherwise.


void popContext();

Revert to the previous Namespace context.

Normally, you should pop the context at the end of each XML element. After popping the context, all Namespace prefix mappings that were previously in force are restored.

You must not attempt to declare additional Namespace prefixes after popping a context, unless you push another context first.


bool processName(
    const XMLString & qname,
    XMLString & namespaceURI,
    XMLString & localName,
    bool isAttribute
) const;

Process a raw XML 1.0 name. This method processes a raw XML 1.0 name in the current context by removing the prefix and looking it up among the prefixes currently declared. The result will be returned in namespaceURI and localName. If the raw name has a prefix that has not been declared, then the return value will be false, otherwise true.

Note that attribute names are processed differently than element names: an unprefixed element name will receive the default Namespace (if any), while an unprefixed attribute name will not.


void pushContext();

Start a new Namespace context. The new context will automatically inherit the declarations of its parent context, but it will also keep track of which declarations were made within this context.

Event callback code should start a new context once per element. This means being ready to call this in either of two places. For elements that don't include namespace declarations, the ContentHandler::startElement() callback is the right place. For elements with such a declaration, it'd done in the first ContentHandler::startPrefixMapping() callback. A boolean flag can be used to track whether a context has been started yet. When either of those methods is called, it checks the flag to see if a new context needs to be started. If so, it starts the context and sets the flag. After ContentHandler::startElement() does that, it always clears the flag.

Normally, SAX drivers would push a new context at the beginning of each XML element. Then they perform a first pass over the attributes to process all namespace declarations, making ContentHandler::startPrefixMapping() callbacks. Then a second pass is made, to determine the namespace-qualified names for all attributes and for the element name. Finally all the information for the ContentHandler::startElement() callback is available, so it can then be made.

The Namespace support object always starts with a base context already in force: in this context, only the "xml" prefix is declared.


void reset();

Reset this Namespace support object for reuse.

It is necessary to invoke this method before reusing the Namespace support object for a new session. If namespace declaration URIs are to be supported, that flag must also be set to a non-default value. Reset this Namespace support object for reuse.


bool undeclarePrefix(
    const XMLString & prefix

Remove the given namespace prefix.



static const XMLString XMLNS_NAMESPACE;




static const XMLString XML_NAMESPACE;


static const XMLString XML_NAMESPACE_PREFIX;