<?xml version="1.0" standalone="no"?>
<!DOCTYPE s1 SYSTEM "./dtd/document.dtd">
<s1 title="Programming Guide">
<p>This page has sections on the following topics:</p>
<ul>
<li><link anchor="SAX1ProgGuide">SAX Programming Guide</link></li>
<ul>
<li><link anchor="ConstructParser">Constructing a parser</link></li>
<li><link anchor="UsingSAX1API">Using the SAX API</link></li>
</ul>
<li><link anchor="SAX2ProgGuide">SAX2 Programming Guide</link></li>
<ul>
<li><link anchor="ConstructParser2">Constructing an XML Reader</link></li>
<li><link anchor="UsingSAX2API">Using the SAX2 API</link></li>
<li><link anchor="SAX2Features">Supported Features</link></li>
</ul>
<li><link anchor="DOMProgGuide">DOM Programming Guide</link></li>
<ul>
<li><link anchor="JAVAandCPP">Comparision of Java and C++ DOM's</link></li>
<ul>
<li><link anchor="AccessAPI">Accessing the API from application code</link></li>
<li><link anchor="ClassNames">Class Names</link></li>
<li><link anchor="ObjMemMgmt">Objects and Memory Management</link></li>
</ul>
<li><link anchor="DOMString">DOMString</link></li>
<ul>
<li><link anchor="EqualityTesting">Equality Testing</link></li>
</ul>
<li><link anchor="Downcasting">Downcasting</link></li>
<li><link anchor="Subclassing">Subclassing</link></li>
</ul>
<li><link anchor="IDOMProgGuide">Experimental IDOM Programming Guide</link></li>
<ul>
<li><link anchor="ConstructIDOMParser">Constructing a parser</link></li>
<li><link anchor="DOMandIDOM">Comparision of C++ DOM and IDOM</link></li>
<ul>
<li><link anchor="Motivation">Motivation behind new design</link></li>
<li><link anchor="IDOMClassNames">Class Names</link></li>
<li><link anchor="IDOMObjMgmt">Objects Management</link></li>
<li><link anchor="IDOMMemMgmt">Memory Management</link></li>
<ul>
<li><link anchor="IDOMMemImplicit">Implicit Object Deletion</link></li>
<li><link anchor="IDOMMemExplicit">Explicit Object Deletion</link></li>
</ul>
<li><link anchor="DOMStringXMCh">DOMString vs. XMLCh</link></li>
</ul>
</ul>
</ul>
<anchor name="SAX1ProgGuide"/>
<s2 title="SAX1 Programming Guide">
<anchor name="ConstructParser"/>
<s3 title="Constructing a parser">
<p>In order to use &XercesCName; to parse XML files, you will
need to create an instance of the SAXParser class. The example
below shows the code you need in order to create an instance
of SAXParser. The DocumentHandler and ErrorHandler instances
required by the SAX API are provided using the HandlerBase
class supplied with &XercesCName;.</p>
<source>int main (int argc, char* args[]) {
try {
XMLPlatformUtils::Initialize();
}
catch (const XMLException& toCatch) {
cout << "Error during initialization! :\n"
<< toCatch.getMessage() << "\n";
return 1;
}
char* xmlFile = "x1.xml";
SAXParser* parser = new SAXParser();
parser->setDoValidation(true); // optional.
parser->setDoNamespaces(true); // optional
DocumentHandler* docHandler = new HandlerBase();
ErrorHandler* errHandler = (ErrorHandler*) docHandler;
parser->setDocumentHandler(docHandler);
parser->setErrorHandler(errHandler);
try {
parser->parse(xmlFile);
}
catch (const XMLException& toCatch) {
cout << "\nFile not found: '" << xmlFile << "'\n"
<< "Exception message is: \n"
<< toCatch.getMessage() << "\n" ;
return -1;
}
}</source>
</s3>
<anchor name="UsingSAX1API"/>
<s3 title="Using the SAX API">
<p>The SAX API for XML parsers was originally developed for
Java. Please be aware that there is no standard SAX API for
C++, and that use of the &XercesCName; SAX API does not
guarantee client code compatibility with other C++ XML
parsers.</p>
<p>The SAX API presents a callback based API to the parser. An
application that uses SAX provides an instance of a handler
class to the parser. When the parser detects XML constructs,
it calls the methods of the handler class, passing them
information about the construct that was detected. The most
commonly used handler classes are DocumentHandler which is
called when XML constructs are recognized, and ErrorHandler
which is called when an error occurs. The header files for the
various SAX handler classes are in
'<&XercesCInstallDir;>/include/sax'</p>
<p>As a convenience, &XercesCName; provides the class
HandlerBase, which is a single class which is publicly derived
from all the Handler classes. HandlerBase's default
implementation of the handler callback methods is to do
nothing. A convenient way to get started with &XercesCName; is
to derive your own handler class from HandlerBase and override
just those methods in HandlerBase which you are interested in
customizing. This simple example shows how to create a handler
which will print element names, and print fatal error
messages. The source code for the sample applications show
additional examples of how to write handler classes.</p>
<p>This is the header file MySAXHandler.hpp:</p>
<source>#include <sax/HandlerBase.hpp>
class MySAXHandler : public HandlerBase {
public:
void startElement(const XMLCh* const, AttributeList&);
void fatalError(const SAXParseException&);
};</source>
<p>This is the implementation file MySAXHandler.cpp:</p>
<source>#include "MySAXHandler.hpp"
#include <iostream.h>
MySAXHandler::MySAXHandler()
{
}
MySAXHandler::startElement(const XMLCh* const name,
AttributeList& attributes)
{
// transcode() is an user application defined function which
// converts unicode strings to usual 'char *'. Look at
// the sample program SAXCount for an example implementation.
cout << "I saw element: " << transcode(name) << endl;
}
MySAXHandler::fatalError(const SAXParseException& exception)
{
cout << "Fatal Error: " << transcode(exception.getMessage())
<< " at line: " << exception.getLineNumber()
<< endl;
}</source>
<p>The XMLCh and AttributeList types are supplied by
&XercesCName; and are documented in the include
files. Examples of their usage appear in the source code to
the sample applications.</p>
</s3>
</s2>
<anchor name="SAX2ProgGuide"/>
<s2 title="SAX2 Programming Guide">
<anchor name="ConstructParser2"/>
<s3 title="Constructing an XML Reader">
<p>In order to use &XercesCName; to parse XML files, you will
need to create an instance of the SAX2XMLReader class. The example
below shows the code you need in order to create an instance
of SAX2XMLReader. The ContentHandler and ErrorHandler instances
required by the SAX API are provided using the DefaultHandler
class supplied with &XercesCName;.</p>
<source>int main (int argc, char* args[]) {
try {
XMLPlatformUtils::Initialize();
}
catch (const XMLException& toCatch) {
cout << "Error during initialization! :\n"
<< toCatch.getMessage() << "\n";
return 1;
}
char* xmlFile = "x1.xml";
SAX2XMLReader* parser = XMLReaderFactory::createXMLReader();
parser->setFeature(XMLString::transcode("http://xml.org/sax/features/validation", true) // optional
parser->setFeature(XMLString::transcode("http://xml.org/sax/features/namespaces", true) // optional
ContentHandler* contentHandler = new DefaultHandler();
ErrorHandler* errHandler = (ErrorHandler*) contentHandler;
parser->setContentHandler(contentHandler);
parser->setErrorHandler(errHandler);
try {
parser->parse(xmlFile);
}
catch (const XMLException& toCatch) {
cout << "\nFile not found: '" << xmlFile << "'\n"
<< "Exception message is: \n"
<< toCatch.getMessage() << "\n" ;
return -1;
}
}</source>
</s3>
<anchor name="UsingSAX2API"/>
<s3 title="Using the SAX2 API">
<p>The SAX2 API for XML parsers was originally developed for
Java. Please be aware that there is no standard SAX2 API for
C++, and that use of the &XercesCName; SAX2 API does not
guarantee client code compatibility with other C++ XML
parsers.</p>
<p>The SAX2 API presents a callback based API to the parser. An
application that uses SAX2 provides an instance of a handler
class to the parser. When the parser detects XML constructs,
it calls the methods of the handler class, passing them
information about the construct that was detected. The most
commonly used handler classes are ContentHandler which is
called when XML constructs are recognized, and ErrorHandler
which is called when an error occurs. The header files for the
various SAX2 handler classes are in
'<&XercesCInstallDir;>/include/sax2'</p>
<p>As a convenience, &XercesCName; provides the class
DefaultHandler, which is a single class which is publicly derived
from all the Handler classes. DefaultHandler's default
implementation of the handler callback methods is to do
nothing. A convenient way to get started with &XercesCName; is
to derive your own handler class from DefaultHandler and override
just those methods in HandlerBase which you are interested in
customizing. This simple example shows how to create a handler
which will print element names, and print fatal error
messages. The source code for the sample applications show
additional examples of how to write handler classes.</p>
<p>This is the header file MySAX2Handler.hpp:</p>
<source>#include <sax2/DefaultHandler.hpp>
class MySAX2Handler : public DefaultHandler {
public:
void startElement(
const XMLCh* const uri,
const XMLCh* const localname,
const XMLCh* const qname,
const Attributes& attrs
);
void fatalError(const SAXParseException&);
};</source>
<p>This is the implementation file MySAX2Handler.cpp:</p>
<source>#include "MySAX2Handler.hpp"
#include <iostream.h>
MySAX2Handler::MySAX2Handler()
{
}
MySAX2Handler::startElement(const XMLCh* const uri,
const XMLCh* const localname,
const XMLCh* const qname,
const Attributes& attrs)
{
// transcode() is an user application defined function which
// converts unicode strings to usual 'char *'. Look at
// the sample program SAX2Count for an example implementation.
cout << "I saw element: " << transcode(qname) << endl;
}
MySAX2Handler::fatalError(const SAXParseException& exception)
{
cout << "Fatal Error: " << transcode(exception.getMessage())
<< " at line: " << exception.getLineNumber()
<< endl;
}</source>
<p>The XMLCh and Attributes types are supplied by
&XercesCName; and are documented in the include
files. Examples of their usage appear in the source code to
the sample applications.</p>
</s3>
<anchor name="SAX2Features"/>
<s3 title="Xerces SAX2 Supported Features">
<p>The behavior of the SAX2XMLReader is dependant on the values of the following features.
All of the features below can be set using the <code>SAX2XMLReader::setFeature(XMLCh*,bool)</code> function.
None of these features can be modified in the middle of a parse, or an exception will be thrown.</p>
<table>
<tr><td colspan="2"><em>http://xml.org/sax/features/namespaces</em></td></tr>
<tr><td><em>true:</em></td><td> Perform Namespace processing (default)</td></tr>
<tr><td><em>false:</em></td><td> Optionally do not perform Namespace processing</td></tr>
</table>
<p/>
<table>
<tr><td colspan="2"><em>http://xml.org/sax/features/namespace-prefixes</em></td></tr>
<tr><td><em>true:</em></td><td> Report the orignal prefixed names and attributes used for Namespace declarations (default)</td></tr>
<tr><td><em>false:</em></td><td> Do not report attributes used for Namespace declarations, and optionally do not report original prefixed names. </td></tr>
</table>
<p/>
<table>
<tr><td colspan="2"><em>http://xml.org/sax/features/validation</em></td></tr>
<tr><td><em>true:</em></td><td> Report all validation errors. (default)</td></tr>
<tr><td><em>false:</em></td><td> Do not report validation errors. </td></tr>
</table>
<p/>
<table>
<tr><td colspan="2"><em>http://apache.org/xml/features/validation/dynamic</em></td></tr>
<tr><td><em>true:</em></td><td> The parser will validate the document only if a grammar is specified. (http://xml.org/sax/features/validation must be true)</td></tr>
<tr><td><em>false:</em></td><td> Validation is determined by the state of the http://xml.org/sax/features/validation feature (default)</td></tr>
</table>
<p/>
<table>
<tr><td colspan="2"><em>http://apache.org/xml/features/validation/schema</em></td></tr>
<tr><td><em>true:</em></td><td> Enable the parser's schema support. (default) </td></tr>
<tr><td><em>false:</em></td><td> Disable the parser's schema support. </td></tr>
</table>
<p/>
<table>
<tr><td colspan="2"><em>http://apache.org/xml/features/validation/schema-full-checking</em></td></tr>
<tr><td><em>true:</em></td><td> Enable full schema constraint checking, including checking
which may be time-consuming or memory intensive. Currently, particle unique
attribution constraint checking and particle derivation resriction checking
are controlled by this option. </td></tr>
<tr><td><em>false:</em></td><td> Disable full schema constraint checking (default). </td></tr>
</table>
<p/>
<table>
<tr><td colspan="2"><em>http://apache.org/xml/features/validation/reuse-grammar</em></td></tr>
<tr><td><em>true:</em></td><td> The parser will reuse grammar information from previous parses in subsequent parses. </td></tr>
<tr><td><em>false:</em></td><td> The parser will not reuse any grammar information. (default)</td></tr>
</table>
<p/>
<table>
<tr><td colspan="2"><em>http://apache.org/xml/features/validation/reuse-validator</em> (deprecated)</td></tr>
<tr><td><em>true:</em></td><td> The parser will reuse grammar information from previous parses in subsequent parses. </td></tr>
<tr><td><em>false:</em></td><td> The parser will not reuse any grammar information. (default)</td></tr>
</table>
</s3>
</s2>
<anchor name="DOMProgGuide"/>
<s2 title="DOM Programming Guide">
<anchor name="JAVAandCPP"/>
<s3 title="Java and C++ DOM comparisons">
<p>The C++ DOM API is very similar in design and use, to the
Java DOM API bindings. As a consequence, conversion of
existing Java code that makes use of the DOM to C++ is a
straight forward process.
</p>
<p>
This section outlines the differences between Java and C++ bindings.
</p>
</s3>
<anchor name="AccessAPI"/>
<s3 title="Accessing the API from application code">
<source>
// C++
#include <dom/DOM.hpp></source>
<source>// Java
import org.w3c.dom.*</source>
<p>The header file <dom/DOM.hpp> includes all the
individual headers for the DOM API classes. </p>
</s3>
<anchor name="ClassNames"/>
<s3 title="Class Names">
<p>The C++ class names are prefixed with "DOM_". The intent is
to prevent conflicts between DOM class names and other names
that may already be in use by an application or other
libraries that a DOM based application must link with.</p>
<p>The use of C++ namespaces would also have solved this
conflict problem, but for the fact that many compilers do not
yet support them.</p>
<source>DOM_Document myDocument; // C++
DOM_Node aNode;
DOM_Text someText;</source>
<source>Document myDocument; // Java
Node aNode;
Text someText;</source>
<p>If you wish to use the Java class names in C++, then you need
to typedef them in C++. This is not advisable for the general
case - conflicts really do occur - but can be very useful when
converting a body of existing Java code to C++.</p>
<source>typedef DOM_Document Document;
typedef DOM_Node Node;
Document myDocument; // Now C++ usage is
// indistinguishable from Java
Node aNode;</source>
</s3>
<anchor name="ObjMemMgmt"/>
<s3 title="Objects and Memory Management">
<p>The C++ DOM implementation uses automatic memory management,
implemented using reference counting. As a result, the C++
code for most DOM operations is very similar to the equivalent
Java code, right down to the use of factory methods in the DOM
document class for nearly all object creation, and the lack of
any explicit object deletion.</p>
<p>Consider the following code snippets </p>
<source>// This is C++
DOM_Node aNode;
aNode = someDocument.createElement("ElementName");
DOM_Node docRootNode = someDoc.getDocumentElement();
docRootNode.AppendChild(aNode);</source>
<source>// This is Java
Node aNode;
aNode = someDocument.createElement("ElementName");
Node docRootNode = someDoc.getDocumentElement();
docRootNode.AppendChild(aNode);</source>
<p>The Java and the C++ are identical on the surface, except for
the class names, and this similarity remains true for most DOM
code. </p>
<p>However, Java and C++ handle objects in somewhat different
ways, making it important to understand a little bit of what
is going on beneath the surface.</p>
<p>In Java, the variable <code>aNode</code> is an object reference ,
essentially a pointer. It is initially == null, and references
an object only after the assignment statement in the second
line of the code.</p>
<p>In C++ the variable <code>aNode</code> is, from the C++ language's
perspective, an actual live object. It is constructed when the
first line of the code executes, and DOM_Node::operator = ()
executes at the second line. The C++ class DOM_Node
essentially a form of a smart-pointer; it implements much of
the behavior of a Java Object Reference variable, and
delegates the DOM behaviors to an implementation class that
lives behind the scenes. </p>
<p>Key points to remember when using the C++ DOM classes:</p>
<ul>
<li>Create them as local variables, or as member variables of
some other class. Never "new" a DOM object into the heap or
make an ordinary C pointer variable to one, as this will
greatly confuse the automatic memory management. </li>
<li>The "real" DOM objects - nodes, attributes, CData
sections, whatever, do live on the heap, are created with the
create... methods on class DOM_Document. DOM_Node and the
other DOM classes serve as reference variables to the
underlying heap objects.</li>
<li>The visible DOM classes may be freely copied (assigned),
passed as parameters to functions, or returned by value from
functions.</li>
<li>Memory management of the underlying DOM heap objects is
automatic, implemented by means of reference counting. So long
as some part of a document can be reached, directly or
indirectly, via reference variables that are still alive in
the application program, the corresponding document data will
stay alive in the heap. When all possible paths of access have
been closed off (all of the application's DOM objects have
gone out of scope) the heap data itself will be automatically
deleted. </li>
<li>There are restrictions on the ability to subclass the DOM
classes. </li>
</ul>
</s3>
<anchor name="DOMString"/>
<s3 title="DOMString">
<p>Class DOMString provides the mechanism for passing string
data to and from the DOM API. DOMString is not intended to be
a completely general string class, but rather to meet the
specific needs of the DOM API.</p>
<p>The design derives from two primary sources: from the DOM's
CharacterData interface and from class <code>java.lang.string</code>.</p>
<p>Main features are:</p>
<ul>
<li>It stores Unicode text.</li>
<li>Automatic memory management, using reference counting.</li>
<li>DOMStrings are mutable - characters can be inserted,
deleted or appended.</li>
</ul>
<p></p>
<p>When a string is passed into a method of the DOM, when
setting the value of a Node, for example, the string is cloned
so that any subsequent alteration or reuse of the string by
the application will not alter the document contents.
Similarly, when strings from the document are returned to an
application via the DOM API, the string is cloned so that the
document can not be inadvertently altered by subsequent edits
to the string.</p>
<note>The ICU classes are a more general solution to UNICODE
character handling for C++ applications. ICU is an Open
Source Unicode library, available at the <jump
href="http://oss.software.ibm.com/icu/">IBM
DeveloperWorks website</jump>.</note>
</s3>
<anchor name="EqualityTesting"/>
<s3 title="Equality Testing">
<p>The DOMString equality operators (and all of the rest of the
DOM class conventions) are modeled after the Java
equivalents. The equals() method compares the content of the
string, while the == operator checks whether the string
reference variables (the application program variables) refer
to the same underlying string in memory. This is also true of
DOM_Node, DOM_Element, etc., in that operator == tells whether
the variables in the application are referring to the same
actual node or not. It's all very Java-like </p>
<ul>
<li>bool operator == () is true if the DOMString variables
refer to the same underlying storage. </li>
<li>bool equals() is true if the strings contain the same
characters. </li>
</ul>
<p>Here is an example of how the equality operators work: </p>
<source>DOMString a = "Hello";
DOMString b = a;
DOMString c = a.clone();
if (b == a) // This is true
if (a == c) // This is false
if (a.equals(c)) // This is true
b = b + " World";
if (b == a) // Still true, and the string's
// value is "Hello World"
if (a.equals(c)) // false. a is "Hello World";
// c is still "Hello".</source>
</s3>
<anchor name="Downcasting"/>
<s3 title="Downcasting">
<p>Application code sometimes must cast an object reference from
DOM_Node to one of the classes deriving from DOM_Node,
DOM_Element, for example. The syntax for doing this in C++ is
different from that in Java.</p>
<source>// This is C++
DOM_Node aNode = someFunctionReturningNode();
DOM_Element el = (Element &) aNode;</source>
<source>// This is Java
Node aNode = someFunctionReturningNode();
Element el = (Element) aNode;</source>
<p>The C++ cast is not type-safe; the Java cast is checked for
compatible types at runtime. If necessary, a type-check can
be made in C++ using the node type information: </p>
<source>// This is C++
DOM_Node aNode = someFunctionReturningNode();
DOM_Element el; // by default, el will == null.
if (anode.getNodeType() == DOM_Node::ELEMENT_NODE)
el = (Element &) aNode;
else
// aNode does not refer to an element.
// Do something to recover here.</source>
</s3>
<anchor name="Subclassing"/>
<s3 title="Subclassing">
<p>The C++ DOM classes, DOM_Node, DOM_Attr, DOM_Document, etc.,
are not designed to be subclassed by an application
program. </p>
<p>As an alternative, the DOM_Node class provides a User Data
field for use by applications as a hook for extending nodes by
referencing additional data or objects. See the API
description for DOM_Node for details.</p>
</s3>
</s2>
<anchor name="IDOMProgGuide"/>
<s2 title="Experimental IDOM Programming Guide">
<p>The experimental IDOM API is a new design of the C++ DOM API.
Please note that this experimental IDOM API is only a prototype
and is subject to change.</p>
<anchor name="ConstructIDOMParser"/>
<s3 title="Constructing a parser">
<p>In order to use &XercesCName; to parse XML files using IDOM, you
will need to create an instance of the IDOMParser class. The example
below shows the code you need in order to create an instance of the
IDOMParser.</p>
<source>
int main (int argc, char* args[]) {
try {
XMLPlatformUtils::Initialize();
}
catch (const XMLException& toCatch) {
cout << "Error during initialization! :\n"
<< toCatch.getMessage() << "\n";
return 1;
}
char* xmlFile = "x1.xml";
IDOMParser* parser = new IDOMParser();
parser->setValidationScheme(IDOMParser::Val_Always); // optional.
parser->setDoNamespaces(true); // optional
ErrorHandler* errHandler = (ErrorHandler*) new HandlerBase();
parser->setErrorHandler(errHandler);
try {
parser->parse(xmlFile);
}
catch (const XMLException& toCatch) {
cout << "\nFile not found: '" << xmlFile << "'\n"
<< "Exception message is: \n"
<< toCatch.getMessage() << "\n" ;
return -1;
}
return 0;
}
</source>
</s3>
<anchor name="DOMandIDOM"/>
<s3 title="Comparision of C++ DOM and IDOM">
<p>
This section outlines the differences between the C++ DOM and IDOM APIs.
</p>
</s3>
<anchor name="Motivation"/>
<s3 title="Motivation behind new design">
<p>
The performance of the C++ DOM has not been as good as it
might be, especially for use in server style applications.
The DOM's reference counted automatic memory management has
been the biggest time consumer. The situation becomes worse
when running multi-threaded applications.
</p>
<p>
The experimental C++ IDOM is a new alternative to the C++ DOM, and aims at
meeting the following requirements:
</p>
<ul>
<li>Reduced memory footprint.</li>
<li>Fast.</li>
<li>Good scalability on multiprocessor systems.</li>
<li>More C++ like and less Java like.</li>
</ul>
</s3>
<anchor name="IDOMClassNames"/>
<s3 title="Class Names">
<p>
The IDOM class names are prefixed with "IDOM_". The intent is
to prevent conflicts between IDOM class names and DOM class names
that may already be in use by an application or other
libraries that a DOM based application must link with.
</p>
<source>
IDOM_Document* myDocument; // IDOM
IDOM_Node* aNode;
IDOM_Text* someText;
</source>
<source>
DOM_Document myDocument; // DOM
DOM_Node aNode;
DOM_Text someText;
</source>
</s3>
<anchor name="IDOMObjMgmt"/>
<s3 title="Objects Management">
<p>Applications would use normal C++ pointers to directly access the
implementation objects for Nodes in IDOM C++, while they would use
object references in DOM C++.
</p>
<p>Consider the following code snippets</p>
<source>
// IDOM C++
IDOM_Node* aNode;
IDOM_Node* docRootNode;
aNode = someDocument->createElement("ElementName");
docRootNode = someDocument->getDocumentElement();
docRootNode->appendChild(aNode);
</source>
<source>
// DOM C++
DOM_Node aNode;
DOM_Node docRootNode;
aNode = someDocument.createElement("ElementName");
docRootNode = someDocument.getDocumentElement();
docRootNode.appendChild(aNode);
</source>
</s3>
<anchor name="IDOMMemMgmt"/>
<s3 title="Memory Management">
<p>The C++ IDOM implementation no longer uses reference counting for
automatic memory management. The C++ IDOM uses an independent storage
allocator per document. The storage for a DOM document is
associated with the document node object.
The advantage here is that allocation would require no synchronization
in most cases (based on the the same threading model that we
have now - one thread active per document, but any number of
documents running in parallel with separate threads).
</p>
<p>The allocator does not support a delete operation at all - all
allocated memory would persist for the life of the document, and
then the larger blocks would be returned to the system without separately
deleting all of the individual nodes and strings within the document.
</p>
<p>The C++ DOM and IDOM are similar in the use of factory methods in the
document class for all object creation. They differ in the object deletion
mechanism.
</p>
<p>In C++ DOM, there is no explicit object deletion. The deallocation of
memory is automatically taken care of by the reference counting.
</p>
<p>In C++ IDOM, there is an implict and explict object deletion.
</p>
</s3>
<anchor name="IDOMMemImplicit"/>
<s3 title="Implicit Object Deletion">
<p>When parsing a document using an IDOMParser, all memory allocated
for a DOM tree is associated to the DOM document. And this storage
will be automatically deleted when the parser instance is deleted (implicit).
</p>
<p>If you do multiple parse using the same IDOMParser instance, then
multiple DOM documents will be generated and saved in a vector pool.
All these documents (and thus all the allocated memory) won't be deleted
until the parser instance is destroyed. If you want to release the memory
back to the system but don't want to destroy the IDOMParser instance at this moment,
then you can call the method IDOMParser::resetDocumentPool to reset the document
vector pool, provided that you do not need access to these documents anymore.
</p>
<p>Consider the following code snippets: </p>
<source>
// C++ IDOM - implicit deletion
IDOMParser* parser = new IDOMParser();
parser->parse(xmlFile)
IDOM_Document *doc = parser->getDocument();
unsigned int i = 1000;
while (i > 0) {
parser->parse(xmlFile)
IDOM_Document* myDoc = parser->getDocument();
i--;
}
// all allocated memory associated with these 1001 DOM documents
// will be deleted implicitly when the parser instance is destroyed
delete parser;
</source>
<source>
// C++ IDOM - implicit deletion
// optionally release the memory
IDOMParser* parser = new IDOMParser();
unsigned int i = 1000;
while (i > 0) {
parser->parse(xmlFile)
IDOM_Document *doc = parser->getDocument();
i--;
}
// instead of waiting until the parser instance is destroyed,
// user can optionally choose to release the memory back to the system
// if does not need access to these 1000 parsed documents anymore.
parser->resetDocumentPool();
// now the parser has some fresh memory to work on for the following
// big loop
i = 1000;
while (i > 0) {
parser->parse(xmlFile)
IDOM_Document *doc = parser->getDocument();
i--;
}
delete parser;
</source>
</s3>
<anchor name="IDOMMemExplicit"/>
<s3 title="Explicit Object Deletion">
<p>If user is manually building a DOM tree in memory using the document factory methods,
then the user needs to explicilty delete the document object to free all the allocated memory.
It normally falls under the following 3 scenarios:
</p>
<ul>
<li>If a user is manually creating a DOM document using the document implementation
factory methods, IDOM_DOMImplementation::getImplementation()->createDocument,
then the user needs to explicilty delete the document object to free all
allocated memory. </li>
<li>If a user is creating a DocumentType object using the document implementation factory
method, IDOM_DOMImplementation::getImplementation()->createDocumentType, then
the user also needs to explicilty delete the document type object to free the
allocated memory.</li>
<li>Special case: If a user is creating a DocumentType using the document
implementation factory method, and clone the node WITHOUT assigning a document
owner to that documentType object, then the cloned node also needs to be explicitly
deleted.</li>
</ul>
<p>Consider the following code snippets: </p>
<source>
// C++ IDOM - explicit deletion
// use the document implementation factory method to create a document type and a document
IDOM_DocumentType* myDocType;
IDOM_Document* myDocument;
IDOM_Node* root;
IDOM_Node* aNode;
myDocType = IDOM_DOMImplementation::getImplementation()->createDocumentType(name, 0, 0);
myDocument = IDOM_DOMImplementation::getImplementation()->createDocument(0, name, myDocType);
root = myDocument->getDocumentElement();
aNode = myDocument->createElement(anElementname);
root->appendChild(aNode);
// need to delete both myDocType and myDocument which are created through DOM Implementation
delete myDocType;
delete myDocument;
</source>
<source>
// C++ IDOM - explicit deletion
// use the document implementation factory method to create a document
IDOM_DocumentType* myDocType;
IDOM_Document* myDocument;
IDOM_Node* root;
IDOM_Node* aNode;
myDocument = IDOM_DOMImplementation::getImplementation()->createDocument();
myDocType = myDocument->createDocumentType(name);
root = myDocument->createElement(name);
aNode = myDocument->createElement(anElementname);
myDocument->appendChild(myDocType);
myDocument->appendChild(root);
root->appendChild(aNode);
// the myDocType is created through myDocument, not through Document Implementation
// thus no need to delete myDocType
delete myDocument;
</source>
<source>
// C++ IDOM - explicit deletion
// manually build a DOM document
// clone the document type object which does not have an owner yet
IDOM_DocumentType* myDocType1;
IDOM_DocumentType* myDocType;
IDOM_Document* myDocument;
IDOM_Node* root;
IDOM_Node* aNode;
myDocType = IDOM_DOMImplementation::getImplementation()->createDocumentType(name, 0, 0);
myDocType1 = (IDOM_DocumentType*) myDocType->cloneNode(false);
myDocument = IDOM_DOMImplementation::getImplementation()->createDocument(0, name, myDocType);
root = myDocument->getDocumentElement();
aNode = myDocument->createElement(anElementname);
root->appendChild(aNode);
// myDocType does not have an owner yet when myDocType1 was cloned.
// thus need to explicitly delete myDocType1
delete myDocType1;
delete myDocType;
delete myDocument;
</source>
<source>
// C++ IDOM - explicit deletion
// manually build a DOM document
// clone the document type object that has an owner already
// thus no need to delete the cloned object
IDOM_DocumentType* myDocType1;
IDOM_DocumentType* myDocType;
IDOM_Document* myDocument;
IDOM_Node* root;
IDOM_Node* aNode;
myDocType = IDOM_DOMImplementation::getImplementation()->createDocumentType(name, 0, 0);
myDocument = IDOM_DOMImplementation::getImplementation()->createDocument(0, name, myDocType);
myDocType1 = (IDOM_DocumentType*) myDocType->cloneNode(false);
root = myDocument->getDocumentElement();
aNode = myDocument->createElement(anElementname);
root->appendChild(aNode);
// myDocType already has myDocument as the owner when myDocType1 was cloned
// thus NO need to explicitly delete myDocType1
delete myDocType;
delete myDocument;
</source>
</s3>
<p>Key points to remember when using the C++ IDOM classes:</p>
<ul>
<li>The DOM objects are accessed via C++ pointers.</li>
<li>The DOM objects - nodes, attributes, CData
sections, etc., are created with the factory methods
(create...) in the document class.</li>
<li>If you are manually building a DOM tree in memory, you
need to explicitly delete the document object.
Memory management will be automatically taken care of by
the IDOM parser when parsing an instance document.</li>
</ul>
<anchor name="DOMStringXMCh"/>
<s3 title="DOMString vs. XMLCh">
<p>The IDOM C++ no longer uses DOMString to pass string data to
and from the DOM API. Instead, the IDOM C++ uses plain, null-terminated
(XMLCh *) utf-16 strings. The (XMLCh*) utf-16 type string is much
simpler with lower overhead. All the string data would remain in
memory until the document object is deleted.</p>
<source>
//C++ IDOM
const XMLCh* nodeValue = aNode->getNodeValue();
</source>
<source>
//C++ DOM
DOMString nodeValue = aNode.getNodeValue();
</source>
</s3>
</s2>
</s1>
