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Daniel Veillard	1177ca4	2003-04-26 22:29:54 +0000	[diff] [blame]	1	<?xml version="1.0" encoding="ISO-8859-1"?>
				2	<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
				3	<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" /><link rel="SHORTCUT ICON" href="/favicon.ico" /><style type="text/css">
Daniel Veillard	373a475	2002-02-21 14:46:29 +0000	[diff] [blame]	4	TD {font-family: Verdana,Arial,Helvetica}
				5	BODY {font-family: Verdana,Arial,Helvetica; margin-top: 2em; margin-left: 0em; margin-right: 0em}
				6	H1 {font-family: Verdana,Arial,Helvetica}
				7	H2 {font-family: Verdana,Arial,Helvetica}
				8	H3 {font-family: Verdana,Arial,Helvetica}
Daniel Veillard	b8cfbd1	2001-10-25 10:53:28 +0000	[diff] [blame]	9	A:link, A:visited, A:active { text-decoration: underline }
Daniel Veillard	f781dba	2006-06-09 13:34:49 +0000	[diff] [blame]	10	</style><title>A real example</title></head><body bgcolor="#8b7765" text="#000000" link="#a06060" vlink="#000000"><table border="0" width="100%" cellpadding="5" cellspacing="0" align="center"><tr><td width="120"><a href="http://swpat.ffii.org/"><img src="epatents.png" alt="Action against software patents" /></a></td><td width="180"><a href="http://www.gnome.org/"><img src="gnome2.png" alt="Gnome2 Logo" /></a><a href="http://www.w3.org/Status"><img src="w3c.png" alt="W3C Logo" /></a><a href="http://www.redhat.com/"><img src="redhat.gif" alt="Red Hat Logo" /></a><div align="left"><a href="http://xmlsoft.org/"><img src="Libxml2-Logo-180x168.gif" alt="Made with Libxml2 Logo" /></a></div></td><td><table border="0" width="90%" cellpadding="2" cellspacing="0" align="center" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3" bgcolor="#fffacd"><tr><td align="center"><h1>The XML C parser and toolkit of Gnome</h1><h2>A real example</h2></td></tr></table></td></tr></table></td></tr></table><table border="0" cellpadding="4" cellspacing="0" width="100%" align="center"><tr><td bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="2" width="100%"><tr><td valign="top" width="200" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3"><tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Developer Menu</b></center></td></tr><tr><td bgcolor="#fffacd"><form action="search.php" enctype="application/x-www-form-urlencoded" method="get"><input name="query" type="text" size="20" value="" /><input name="submit" type="submit" value="Search ..." /></form><ul><li><a href="index.html" style="font-weight:bold">Main Menu</a></li><li><a href="html/index.html" style="font-weight:bold">Reference Manual</a></li><li><a href="examples/index.html" style="font-weight:bold">Code Examples</a></li><li><a href="guidelines.html">XML Guidelines</a></li><li><a href="tutorial/index.html">Tutorial</a></li><li><a href="xmlreader.html">The Reader Interface</a></li><li><a href="ChangeLog.html">ChangeLog</a></li><li><a href="XSLT.html">XSLT</a></li><li><a href="python.html">Python and bindings</a></li><li><a href="architecture.html">libxml2 architecture</a></li><li><a href="tree.html">The tree output</a></li><li><a href="interface.html">The SAX interface</a></li><li><a href="xmlmem.html">Memory Management</a></li><li><a href="xmlio.html">I/O Interfaces</a></li><li><a href="library.html">The parser interfaces</a></li><li><a href="entities.html">Entities or no entities</a></li><li><a href="namespaces.html">Namespaces</a></li><li><a href="upgrade.html">Upgrading 1.x code</a></li><li><a href="threads.html">Thread safety</a></li><li><a href="DOM.html">DOM Principles</a></li><li><a href="example.html">A real example</a></li><li><a href="xml.html">flat page</a>, <a href="site.xsl">stylesheet</a></li></ul></td></tr></table><table width="100%" border="0" cellspacing="1" cellpadding="3"><tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>API Indexes</b></center></td></tr><tr><td bgcolor="#fffacd"><ul><li><a href="APIchunk0.html">Alphabetic</a></li><li><a href="APIconstructors.html">Constructors</a></li><li><a href="APIfunctions.html">Functions/Types</a></li><li><a href="APIfiles.html">Modules</a></li><li><a href="APIsymbols.html">Symbols</a></li></ul></td></tr></table><table width="100%" border="0" cellspacing="1" cellpadding="3"><tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Related links</b></center></td></tr><tr><td bgcolor="#fffacd"><ul><li><a href="http://mail.gnome.org/archives/xml/">Mail archive</a></li><li><a href="http://xmlsoft.org/XSLT/">XSLT libxslt</a></li><li><a href="http://phd.cs.unibo.it/gdome2/">DOM gdome2</a></li><li><a href="http://www.aleksey.com/xmlsec/">XML-DSig xmlsec</a></li><li><a href="ftp://xmlsoft.org/">FTP</a></li><li><a href="http://www.zlatkovic.com/projects/libxml/">Windows binaries</a></li><li><a href="http://www.blastwave.org/packages.php/libxml2">Solaris binaries</a></li><li><a href="http://www.explain.com.au/oss/libxml2xslt.html">MacOsX binaries</a></li><li><a href="http://libxmlplusplus.sourceforge.net/">C++ bindings</a></li><li><a href="http://www.zend.com/php5/articles/php5-xmlphp.php#Heading4">PHP bindings</a></li><li><a href="http://sourceforge.net/projects/libxml2-pas/">Pascal bindings</a></li><li><a href="http://libxml.rubyforge.org/">Ruby bindings</a></li><li><a href="http://tclxml.sourceforge.net/">Tcl bindings</a></li><li><a href="http://bugzilla.gnome.org/buglist.cgi?product=libxml2">Bug Tracker</a></li></ul></td></tr></table></td></tr></table></td><td valign="top" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%"><tr><td><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table border="0" cellpadding="3" cellspacing="1" width="100%"><tr><td bgcolor="#fffacd"><p>Here is a real size example, where the actual content of the application
				11	data is not kept in the DOM tree but uses internal structures. It is based on
				12	a proposal to keep a database of jobs related to Gnome, with an XML based
				13	storage structure. Here is an <a href="gjobs.xml">XML encoded jobs
				14	base</a>:</p><pre><?xml version="1.0"?>
Daniel Veillard	024f199	2003-12-10 16:43:49 +0000	[diff] [blame]	15	<gjob:Helping xmlns:gjob="http://www.gnome.org/some-location">
Daniel Veillard	c948420	2001-10-24 12:35:52 +0000	[diff] [blame]	16	<gjob:Jobs>
				17
				18	<gjob:Job>
Daniel Veillard	024f199	2003-12-10 16:43:49 +0000	[diff] [blame]	19	<gjob:Project ID="3"/>
Daniel Veillard	c948420	2001-10-24 12:35:52 +0000	[diff] [blame]	20	<gjob:Application>GBackup</gjob:Application>
				21	<gjob:Category>Development</gjob:Category>
				22
				23	<gjob:Update>
				24	<gjob:Status>Open</gjob:Status>
				25	<gjob:Modified>Mon, 07 Jun 1999 20:27:45 -0400 MET DST</gjob:Modified>
				26	<gjob:Salary>USD 0.00</gjob:Salary>
				27	</gjob:Update>
				28
				29	<gjob:Developers>
				30	<gjob:Developer>
				31	</gjob:Developer>
				32	</gjob:Developers>
				33
				34	<gjob:Contact>
				35	<gjob:Person>Nathan Clemons</gjob:Person>
				36	<gjob:Email>nathan@windsofstorm.net</gjob:Email>
				37	<gjob:Company>
				38	</gjob:Company>
				39	<gjob:Organisation>
				40	</gjob:Organisation>
				41	<gjob:Webpage>
				42	</gjob:Webpage>
				43	<gjob:Snailmail>
				44	</gjob:Snailmail>
				45	<gjob:Phone>
				46	</gjob:Phone>
				47	</gjob:Contact>
				48
				49	<gjob:Requirements>
				50	The program should be released as free software, under the GPL.
				51	</gjob:Requirements>
				52
				53	<gjob:Skills>
				54	</gjob:Skills>
				55
				56	<gjob:Details>
				57	A GNOME based system that will allow a superuser to configure
				58	compressed and uncompressed files and/or file systems to be backed
				59	up with a supported media in the system. This should be able to
				60	perform via find commands generating a list of files that are passed
				61	to tar, dd, cpio, cp, gzip, etc., to be directed to the tape machine
				62	or via operations performed on the filesystem itself. Email
				63	notification and GUI status display very important.
				64	</gjob:Details>
				65
				66	</gjob:Job>
				67
				68	</gjob:Jobs>
Daniel Veillard	f781dba	2006-06-09 13:34:49 +0000	[diff] [blame]	69	</gjob:Helping></pre><p>While loading the XML file into an internal DOM tree is a matter of
				70	calling only a couple of functions, browsing the tree to gather the data and
				71	generate the internal structures is harder, and more error prone.</p><p>The suggested principle is to be tolerant with respect to the input
				72	structure. For example, the ordering of the attributes is not significant,
				73	the XML specification is clear about it. It's also usually a good idea not to
				74	depend on the order of the children of a given node, unless it really makes
				75	things harder. Here is some code to parse the information for a person:</p><pre>/*
Daniel Veillard	c948420	2001-10-24 12:35:52 +0000	[diff] [blame]	76	* A person record
				77	*/
				78	typedef struct person {
				79	char *name;
				80	char *email;
				81	char *company;
				82	char *organisation;
				83	char *smail;
				84	char *webPage;
				85	char *phone;
				86	} person, *personPtr;
				87
				88	/*
				89	* And the code needed to parse it
				90	*/
				91	personPtr parsePerson(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
				92	personPtr ret = NULL;
				93
Daniel Veillard	024f199	2003-12-10 16:43:49 +0000	[diff] [blame]	94	DEBUG("parsePerson\n");
Daniel Veillard	c948420	2001-10-24 12:35:52 +0000	[diff] [blame]	95	/*
				96	* allocate the struct
				97	*/
				98	ret = (personPtr) malloc(sizeof(person));
				99	if (ret == NULL) {
Daniel Veillard	024f199	2003-12-10 16:43:49 +0000	[diff] [blame]	100	fprintf(stderr,"out of memory\n");
Daniel Veillard	c948420	2001-10-24 12:35:52 +0000	[diff] [blame]	101	return(NULL);
				102	}
				103	memset(ret, 0, sizeof(person));
				104
				105	/* We don't care what the top level element name is */
				106	cur = cur->xmlChildrenNode;
				107	while (cur != NULL) {
Daniel Veillard	024f199	2003-12-10 16:43:49 +0000	[diff] [blame]	108	if ((!strcmp(cur->name, "Person")) && (cur->ns == ns))
Daniel Veillard	c948420	2001-10-24 12:35:52 +0000	[diff] [blame]	109	ret->name = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1);
Daniel Veillard	024f199	2003-12-10 16:43:49 +0000	[diff] [blame]	110	if ((!strcmp(cur->name, "Email")) && (cur->ns == ns))
Daniel Veillard	c948420	2001-10-24 12:35:52 +0000	[diff] [blame]	111	ret->email = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1);
				112	cur = cur->next;
				113	}
				114
				115	return(ret);
Daniel Veillard	f781dba	2006-06-09 13:34:49 +0000	[diff] [blame]	116	}</pre><p>Here are a couple of things to notice:</p><ul><li>Usually a recursive parsing style is the more convenient one: XML data
				117	is by nature subject to repetitive constructs and usually exhibits highly
				118	structured patterns.</li>
				119	<li>The two arguments of type <em>xmlDocPtr</em> and <em>xmlNsPtr</em>,
				120	i.e. the pointer to the global XML document and the namespace reserved to
				121	the application. Document wide information are needed for example to
				122	decode entities and it's a good coding practice to define a namespace for
				123	your application set of data and test that the element and attributes
				124	you're analyzing actually pertains to your application space. This is
				125	done by a simple equality test (cur->ns == ns).</li>
				126	<li>To retrieve text and attributes value, you can use the function
				127	<em>xmlNodeListGetString</em> to gather all the text and entity reference
				128	nodes generated by the DOM output and produce an single text string.</li>
				129	</ul><p>Here is another piece of code used to parse another level of the
				130	structure:</p><pre>#include <libxml/tree.h>
Daniel Veillard	c948420	2001-10-24 12:35:52 +0000	[diff] [blame]	131	/*
				132	* a Description for a Job
				133	*/
				134	typedef struct job {
				135	char *projectID;
				136	char *application;
				137	char *category;
				138	personPtr contact;
				139	int nbDevelopers;
				140	personPtr developers[100]; /* using dynamic alloc is left as an exercise */
				141	} job, *jobPtr;
				142
				143	/*
				144	* And the code needed to parse it
				145	*/
				146	jobPtr parseJob(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
				147	jobPtr ret = NULL;
				148
Daniel Veillard	024f199	2003-12-10 16:43:49 +0000	[diff] [blame]	149	DEBUG("parseJob\n");
Daniel Veillard	c948420	2001-10-24 12:35:52 +0000	[diff] [blame]	150	/*
				151	* allocate the struct
				152	*/
				153	ret = (jobPtr) malloc(sizeof(job));
				154	if (ret == NULL) {
Daniel Veillard	024f199	2003-12-10 16:43:49 +0000	[diff] [blame]	155	fprintf(stderr,"out of memory\n");
Daniel Veillard	c948420	2001-10-24 12:35:52 +0000	[diff] [blame]	156	return(NULL);
				157	}
				158	memset(ret, 0, sizeof(job));
				159
				160	/* We don't care what the top level element name is */
				161	cur = cur->xmlChildrenNode;
				162	while (cur != NULL) {
				163
Daniel Veillard	024f199	2003-12-10 16:43:49 +0000	[diff] [blame]	164	if ((!strcmp(cur->name, "Project")) && (cur->ns == ns)) {
				165	ret->projectID = xmlGetProp(cur, "ID");
Daniel Veillard	c948420	2001-10-24 12:35:52 +0000	[diff] [blame]	166	if (ret->projectID == NULL) {
Daniel Veillard	024f199	2003-12-10 16:43:49 +0000	[diff] [blame]	167	fprintf(stderr, "Project has no ID\n");
Daniel Veillard	c948420	2001-10-24 12:35:52 +0000	[diff] [blame]	168	}
				169	}
Daniel Veillard	024f199	2003-12-10 16:43:49 +0000	[diff] [blame]	170	if ((!strcmp(cur->name, "Application")) && (cur->ns == ns))
Daniel Veillard	c948420	2001-10-24 12:35:52 +0000	[diff] [blame]	171	ret->application = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1);
Daniel Veillard	024f199	2003-12-10 16:43:49 +0000	[diff] [blame]	172	if ((!strcmp(cur->name, "Category")) && (cur->ns == ns))
Daniel Veillard	c948420	2001-10-24 12:35:52 +0000	[diff] [blame]	173	ret->category = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1);
Daniel Veillard	024f199	2003-12-10 16:43:49 +0000	[diff] [blame]	174	if ((!strcmp(cur->name, "Contact")) && (cur->ns == ns))
Daniel Veillard	c948420	2001-10-24 12:35:52 +0000	[diff] [blame]	175	ret->contact = parsePerson(doc, ns, cur);
				176	cur = cur->next;
				177	}
				178
				179	return(ret);
Daniel Veillard	f781dba	2006-06-09 13:34:49 +0000	[diff] [blame]	180	}</pre><p>Once you are used to it, writing this kind of code is quite simple, but
				181	boring. Ultimately, it could be possible to write stubbers taking either C
				182	data structure definitions, a set of XML examples or an XML DTD and produce
				183	the code needed to import and export the content between C data and XML
				184	storage. This is left as an exercise to the reader :-)</p><p>Feel free to use <a href="example/gjobread.c">the code for the full C
				185	parsing example</a> as a template, it is also available with Makefile in the
				186	Gnome CVS base under gnome-xml/example</p><p><a href="bugs.html">Daniel Veillard</a></p></td></tr></table></td></tr></table></td></tr></table></td></tr></table></td></tr></table></body></html>