doc/program-others.xml

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<!DOCTYPE s1 SYSTEM "sbk:/style/dtd/document.dtd">

<s1 title="Programming Guide">
    <anchor name="Macro"/>
    <s2 title="Version Macro">
        <p>&XercesCName; has defined a numeric preprocessor macro, _XERCES_VERSION, for users to
           introduce into their code to perform conditional compilation where the
           version of Xerces is detected in order to enable or disable version
          specific capabilities. For example,
         </p>
<source>
       #if _XERCES_VERSION >= 20304
         // code specific to Xerces-C++ version 2.3.4
       #else
         // old code here...
       #endif
</source>
        <p>The minor and revision (patch level) numbers have two digits of resolution
           which means that '3' becomes '03' and '4' becomes '04' in this example.
        </p>
        <p>There are also other string macro, or constants to represent the Xerces-C++ version.
           Please refer to the header xercesc/util/XercesVersion.hpp for further details.
        </p>
    </s2>


    <anchor name="Schema"/>
    <s2 title="Schema Support">
        <p>&XercesCName; contains an implementation of the W3C XML Schema
           Language.  See <jump href="schema.html">the Schema page</jump> for details.
         </p>
    </s2>

    <anchor name="Progressive"/>
    <s2 title="Progressive Parsing">

        <p>In addition to using the <ref>parse()</ref> method to parse an XML File.
        You can use the other two parsing methods, <ref>parseFirst()</ref> and <ref>parseNext()</ref>
        to do 'progressive parsing', so that you don't
        have to depend upon throwing an exception to terminate the
        parsing operation.
         </p>
         <p>
        Calling parseFirst() will cause the DTD (both internal and
        external subsets), and any pre-content, i.e. everything up to
        but not including the root element, to be parsed. Subsequent calls to
        parseNext() will cause one more pieces of markup to be parsed,
        and spit out from the core scanning code to the parser (and
        hence either on to you if using SAX or into the DOM tree if
        using DOM).
         </p>
         <p>
        You can quit the parse any time by just not
        calling parseNext() anymore and breaking out of the loop. When
        you call parseNext() and the end of the root element is the
        next piece of markup, the parser will continue on to the end
        of the file and return false, to let you know that the parse
        is done. So a typical progressive parse loop will look like
        this:</p>

<source>// Create a progressive scan token
XMLPScanToken token;

if (!parser.parseFirst(xmlFile, token))
{
  cerr &lt;&lt; "scanFirst() failed\n" &lt;&lt; endl;
  return 1;
}

//
// We started ok, so lets call scanNext()
// until we find what we want or hit the end.
//
bool gotMore = true;
while (gotMore &amp;&amp; !handler.getDone())
  gotMore = parser.parseNext(token);</source>

        <p>In this case, our event handler object (named 'handler'
        surprisingly enough) is watching form some criteria and will
        return a status from its getDone() method. Since the handler
        sees the SAX events coming out of the SAXParser, it can tell
        when it finds what it wants. So we loop until we get no more
        data or our handler indicates that it saw what it wanted to
        see.</p>

        <p>When doing non-progressive parses, the parser can easily
        know when the parse is complete and insure that any used
        resources are cleaned up. Even in the case of a fatal parsing
        error, it can clean up all per-parse resources. However, when
        progressive parsing is done, the client code doing the parse
        loop might choose to stop the parse before the end of the
        primary file is reached. In such cases, the parser will not
        know that the parse has ended, so any resources will not be
        reclaimed until the parser is destroyed or another parse is started.</p>

        <p>This might not seem like such a bad thing; however, in this case,
        the files and sockets which were opened in order to parse the
        referenced XML entities will remain open. This could cause
        serious problems. Therefore, you should destroy the parser instance
        in such cases, or restart another parse immediately. In a future
        release, a reset method will be provided to do this more cleanly.</p>

        <p>Also note that you must create a scan token and pass it
        back in on each call. This insures that things don't get done
        out of sequence. When you call parseFirst() or parse(), any
        previous scan tokens are invalidated and will cause an error
        if used again. This prevents incorrect mixed use of the two
        different parsing schemes or incorrect calls to
        parseNext().</p>

    </s2>

    <anchor name="GrammarCache"/>
    <s2 title="Preparsing Grammar and Grammar Caching">
        <p>&XercesCName; &XercesCVersion; provides a new function to pre-parse the grammar so that users
           can check for any syntax or error before using the grammar.  Users can also optionally
           cache these pre-parsed grammars for later use during actual parsing.
        </p>
        <p>Here is an example:</p>
<source>
XercesDOMParser parser;

// enbale schema processing
parser.setDoSchema(true);
parser.setDONamespaces(true);

// Let's preparse the schema grammar (.xsd) and cache it.
Grammar* grammar = parser.loadGrammar(xmlFile, Grammar::SchemaGrammarType, true);
</source>
        <p>Besides caching pre-parsed schema grammars, users can also cache any
           grammars encountered during an xml document parse.
        </p>
        <p>Here is an example:</p>
<source>
SAXParser parser;

// Enable grammar caching by setting cacheGrammarFromParse to true.
// The parser will cache any encountered grammars if it does not
// exist in the pool.
// If the grammar is DTD, no internal subset is allowed.
parser.cacheGrammarFromParse(true);

// Let's parse our xml file (DTD grammar)
parser.parse(xmlFile);

// We can get the grammar where the root element was declared
// by calling the parser's method getRootGrammar;
// Note: The parser owns the grammar, and the user should not delete it.
Grammar* grammar = parser.getRootGrammar();
</source>
        <p>We can use any previously cached grammars when parsing new xml
        documents. Here are some examples on how to use those cached grammars:
        </p>
<source>
/**
  * Caching and reusing XML Schema (.xsd) grammar
  * Parse an XML document and cache its grammar set. Then,  use the cached
  * grammar set in subsequent parses.
  */

XercesDOMParser parser;

// Enable schema processing
parser.setDoSchema(true);
parser.setDoNamespaces(true);

// Enable grammar caching
parser.cacheGrammarFromParsing(true);

// Let's parse the XML document. The parser will cache any grammars encounterd.
parser.parse(xmlFile);

// No need to enable re-use by setting useCachedGrammarInParse to true. It is
// automatically enabled with grammar caching.
for (int i=0; i&lt; 3; i++)
    parser.parse(xmlFile);

// This will flush the grammar pool
parser.resetCachedGrammarPool();
</source>

<source>
/**
  * Caching and reusing DTD grammar
  * Preparse a grammar and cache it in the pool. Then, we use the cached grammar
  * when parsing XML documents.
  */

SAX2XMLReader* parser = XMLReaderFactory::createXMLReader();

// Load grammar and cache it
parser->loadGrammar(dtdFile, Grammar::DTDGrammarType, true);

// enable grammar reuse
parser->setFeature(XMLUni::fgXercesUseCachedGrammarInParse, true);

// Parse xml files
parser->parse(xmlFile1);
parser->parse(xmlFile2);
</source>
        <p>There are some limitations about caching and using cached grammars:</p>
           <ul>
              <li>When caching/reusing DTD grammars, no internal subset is allowed.</li>
              <li>When preparsing grammars with caching option enabled, if a grammar, in the
              result set, already exists in the pool (same NS for schema or same system
              id for DTD), the entire set will not be cached.</li>
              <li>When parsing an XML document with the grammar caching option enabled, the
              reuse option is also automatically enabled. We will only parse a grammar if it
              does not exist in the pool.</li>
           </ul>
    </s2>

    <anchor name="LoadableMessageText"/>
    <s2 title="Loadable Message Text">

        <p>The &XercesCName; supports loadable message text.   Although
        the current drop just supports English, it is capable to support other
        languages. Anyone interested in contributing any translations
        should contact us. This would be an extremely useful
        service.</p>

        <p>In order to support the local message loading services, all the error messages
        are captured in an XML file in the src/xercesc/NLS/ directory.
        There is a simple program, in the Tools/NLSXlat/ directory,
        which can spit out that text in various formats. It currently
        supports a simple 'in memory' format (i.e. an array of
        strings), the Win32 resource format, and the message catalog
        format.  The 'in memory' format is intended for very simple
        installations or for use when porting to a new platform (since
        you can use it until you can get your own local message
        loading support done.)</p>

        <p>In the src/xercesc/util/ directory, there is an XMLMsgLoader
        class.  This is an abstraction from which any number of
        message loading services can be derived. Your platform driver
        file can create whichever type of message loader it wants to
        use on that platform.  &XercesCName; currently has versions for the in
        memory format, the Win32 resource format, and the message
        catalog format. An ICU one is present but not implemented
        yet. Some of the platforms can support multiple message
        loaders, in which case a #define token is used to control
        which one is used. You can set this in your build projects to
        control the message loader type used.</p>

    </s2>

    <anchor name="PluggableTranscoders"/>
    <s2 title="Pluggable Transcoders">

        <p>&XercesCName; also supports pluggable transcoding services. The
        XMLTransService class is an abstract API that can be derived
        from, to support any desired transcoding
        service. XMLTranscoder is the abstract API for a particular
        instance of a transcoder for a particular encoding. The
        platform driver file decides what specific type of transcoder
        to use, which allows each platform to use its native
        transcoding services, or the ICU service if desired.</p>

        <p>Implementations are provided for Win32 native services, ICU
        services, and the <ref>iconv</ref> services available on many
        Unix platforms. The Win32 version only provides native code
        page services, so it can only handle XML code in the intrinsic
        encodings ASCII, UTF-8, UTF-16 (Big/Small Endian), UCS4
        (Big/Small Endian), EBCDIC code pages IBM037 and
        IBM1140 encodings, ISO-8859-1 (aka Latin1) and Windows-1252. The ICU version
        provides all of the encodings that ICU supports. The
        <ref>iconv</ref> version will support the encodings supported
        by the local system. You can use transcoders we provide or
        create your own if you feel ours are insufficient in some way,
        or if your platform requires an implementation that &XercesCName; does not
        provide.</p>

    </s2>
</s1>