From bd0f3345a938b35ce6a12f6150373b0955b8dd12 Mon Sep 17 00:00:00 2001 From: Timothy Pearson Date: Sun, 10 Jul 2011 15:24:15 -0500 Subject: Add Qt3 development HEAD version --- doc/html/xml-sax-walkthrough.html | 220 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 220 insertions(+) create mode 100644 doc/html/xml-sax-walkthrough.html (limited to 'doc/html/xml-sax-walkthrough.html') diff --git a/doc/html/xml-sax-walkthrough.html b/doc/html/xml-sax-walkthrough.html new file mode 100644 index 0000000..c0bfdb8 --- /dev/null +++ b/doc/html/xml-sax-walkthrough.html @@ -0,0 +1,220 @@ + + + + + +Walkthrough: How to use the Qt SAX2 classes + + + + + + + +

Walkthrough: How to use the Qt SAX2 classes

+ + +

For a general discussion of the XML topics in Qt please refer to +the document XML Module. +To learn more about SAX2 see the document describing +the Qt SAX2 implementation. +

Before reading on you should at least be familiar with +the Introduction to SAX2. +

A tiny parser

In this section we will present a small example reader that outputs +the names of all elements in an XML document on the command line. +The element names are indented corresponding to their nesting level. +

As mentioned in Introduction to SAX2 +we have to implement the functions of the handler classes that we are +interested in. In our case these are only three: +QXmlContentHandler::startDocument(), +QXmlContentHandler::startElement() and +QXmlContentHandler::endElement(). +

For this purpose we use a subclass of the QXmlDefaultHandler (remember +that the special handler classes are all abstract and the default handler class +provides an implementation that does not change the parsing behavior): +

/****************************************************************************
+** $Id: qt/structureparser.h   3.3.8   edited Jan 11 14:37 $
+**
+** Copyright (C) 1992-2007 Trolltech ASA.  All rights reserved.
+**
+** This file is part of an example program for Qt.  This example
+** program may be used, distributed and modified without limitation.
+**
+*****************************************************************************/
+
+#ifndef STRUCTUREPARSER_H
+#define STRUCTUREPARSER_H
+
+#include <qxml.h>
+
+class QString;
+
+class StructureParser : public QXmlDefaultHandler
+{
+public:
+    bool startDocument();
+    bool startElement( const QString&, const QString&, const QString& ,
+                       const QXmlAttributes& );
+    bool endElement( const QString&, const QString&, const QString& );
+
+private:
+    QString indent;
+};
+
+#endif
+

+ +

Apart from the private helper variable indent that we will use to +get indentation right, there is nothing special about our new +StructureParser class. +

+ +

Even the implementation is straight-forward: +

    #include "structureparser.h"
+
+    #include <stdio.h>
+    #include <qstring.h>
+

First we overload QXmlContentHandler::startDocument() with a non-empty version. +

    bool StructureParser::startDocument()
+    {
+        indent = "";
+        return TRUE;
+    }
+

At the beginning of the document we simply +set indent to an empty string because we +want to print out the root element without any indentation. +Also we return TRUE so that the parser continues without +reporting an error. +

Because we want to be informed when the parser comes +accross a start tag of an element and subsequently print it out, we +have to overload QXmlContentHandler::startElement(). +

    bool StructureParser::startElement( const QString&, const QString&,
+                                        const QString& qName,
+                                        const QXmlAttributes& )
+    {
+        printf( "%s%s\n", (const char*)indent, (const char*)qName );
+        indent += "    ";
+        return TRUE;
+    }
+

This is what the implementation does: The name of the element with +preceding indentation is printed out followed by a linebreak. +Strictly speaking qName contains the local element name +without an eventual prefix denoting the namespace. +

If another element follows before the current element's end tag +it should be indented. Therefore we add four spaces to the +indent string. +

Finally we return TRUE in order to let the parser continue without +errors. +

The last functionality we need to add is the parser's behaviour when an +end tag occurs. This means overloading QXmlContentHandler::endElement(). +

    bool StructureParser::endElement( const QString&, const QString&, const QString& )
+    {
+        indent.remove( (uint)0, 4 );
+        return TRUE;
+    }
+

Obviously we then should shorten the indent string by the four +whitespaces added in startElement(). +

With this we're done with our parser and can start writing the main() +program. +

+ +

    #include "structureparser.h"
+    #include <qfile.h>
+    #include <qxml.h>
+    #include <qwindowdefs.h>
+
+    int main( int argc, char **argv )
+    {
+        if ( argc < 2 ) {
+            fprintf( stderr, "Usage: %s <xmlfile> [<xmlfile> ...]\n", argv[0] );
+            return 1;
+        }
+

This check ensures that we have a sequence of files from the command +line to examine. +

        StructureParser handler;
+

The next step is to create an instance of the StructureParser. +

        QXmlSimpleReader reader;
+        reader.setContentHandler( &handler );
+

After that we set up the reader. As our StructureParser +class deals with QXmlContentHandler functionality only +we simply register it as the content handler of our choice. +

        for ( int i=1; i < argc; i++ ) {
+

Successively we deal with all files given as command line arguments. +

            QFile xmlFile( argv[i] );
+            QXmlInputSource source( &xmlFile );
+

Then we create a +QXmlInputSource for the XML file to be parsed. +

            reader.parse( source );
+

Now we take our input source and start parsing. +

        }
+        return 0;
+    }
+

Running the program on the following XML file... +

<animals>
+<mammals>
+  <monkeys> <gorilla/> <orangutan/> </monkeys>
+</mammals>
+<birds> <pigeon/> <penguin/> </birds>
+</animals>
+
+

+ +

... produces the following output: +

+animals
+    mammals
+        monkeys
+            gorilla
+            orang-utan
+    birds
+        pigeon
+        penguin 
+

+ +

It will however refuse to produce the correct result if you e.g. insert +a whitespace between a < and the element name in your test-XML file. +To prevent such annoyances +you should always install an error handler with QXmlReader::setErrorHandler(). This allows you to report +parsing errors to the user. +