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Re: simple XML for C++ application data-file I/O

• From: Paul Miller <stele@f...>
• To: xml-dev <xml-dev@i...>
• Date: Mon, 06 Dec 1999 09:46:41 -0500

This is what I had in mind. Consider this (contrived) XML data-file,
that consists of a Title, Author, and one or more Paragraph elements:

<Document name="mydoc.doc">
	<Title>Sample XML Document</Title>
	<Author email="paul@f...">Paul Miller</Author>
	<Paragraph>
		This is the first paragraph.
	</Paragraph>
	<Paragraph>
		This is the second paragraph.
	</Paragraph>
</Document>

Now, expat and SAX only give you the elements, so you have to keep track
of where you are in the document in the element handler yourself. What I
have in mind is a nestable set of registered element handlers,
implemented as callbacks. The callbacks are static function pointers,
since I want a non-intrusive design.
With this example, I assume two primary classes (Document and
Paragraph). Although Title and Author are represented as elements here,
they are really attributes of the Document object. Now consider this
code to parse it:

void ParseDocument(XML::InputStream &in)
{
	XML::ElementHandler handlers[] = {
		XML::ElementHandler("Document", sParseDocument),
		XML::ElementHandler::END
	};
	in.Parse(handlers, NULL);	// NULL is optional user-data
}

static void 
sParseDocument(XML::InputStream &in, XML::Element &elem, void *userData)
{
	// query the name attribute
	std::string docName;
	elem.GetAttribute("name", docName);
	// create a new document with this name
	Document *doc = new Document(docName);

	XML::ElementHandler handlers[] = {
		XML::ElementHandler("Title", sParseTitle),
		XML::ElementHandler("Author", sParseAuthor),
		XML::ElementHandler("Paragraph", sParseParagraph),
		XML::ElementHandler::END
	};

	// parse the document elements
	in.Parse(handlers, doc);
}

static void 
Document::sParseTitle(XML::InputStream &in, XML::Element &elem, void
*userData)
{
	Document *doc = (Document *)userData;
	doc->SetTitle(elem.GetData());
}

static void 
Document::sParseAuthor(XML::InputStream &in, XML::Element &elem, void
*userData)
{
	Document *doc = (Document *)userData;
	doc->SetAuthor(elem.GetData(), elem.GetAttribute());
}

static void 
Document::sParseParagraph(XML::InputStream &in, XML::Element &elem, void
*userData)
{
	Document *doc = (Document *)userData;
	Paragraph *para = new Paragraph;
	para->Parse(in, elem);
	doc->AddParagraph(para);
}

void Paragraph::Parse(XML::InputStream &in, XML::Element &elem)
{
	SetText(elem.GetData());
}

The major idea here is you register everything up-front, and
element-specific callbacks get called to deal with specific elements.
You can start up parsing inside an element, so you can nest parsing at
the object level.

Comments?
	
--
Paul Miller - stele@f...

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