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    1 <?xml version="1.0" encoding="UTF-8"?>
    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=UTF-8" /><link rel="SHORTCUT ICON" href="/favicon.ico" /><style type="text/css">
    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}
    9 A:link, A:visited, A:active { text-decoration: underline }
   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://opencsw.org/packages/libxml2">Solaris binaries</a></li><li><a href="http://www.explain.com.au/oss/libxml2xslt.html">MacOsX binaries</a></li><li><a href="http://lxml.de/">lxml Python bindings</a></li><li><a href="http://cpan.uwinnipeg.ca/dist/XML-LibXML">Perl bindings</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>&lt;?xml version="1.0"?&gt;
   15 &lt;gjob:Helping xmlns:gjob="http://www.gnome.org/some-location"&gt;
   16   &lt;gjob:Jobs&gt;
   17 
   18     &lt;gjob:Job&gt;
   19       &lt;gjob:Project ID="3"/&gt;
   20       &lt;gjob:Application&gt;GBackup&lt;/gjob:Application&gt;
   21       &lt;gjob:Category&gt;Development&lt;/gjob:Category&gt;
   22 
   23       &lt;gjob:Update&gt;
   24         &lt;gjob:Status&gt;Open&lt;/gjob:Status&gt;
   25         &lt;gjob:Modified&gt;Mon, 07 Jun 1999 20:27:45 -0400 MET DST&lt;/gjob:Modified&gt;
   26         &lt;gjob:Salary&gt;USD 0.00&lt;/gjob:Salary&gt;
   27       &lt;/gjob:Update&gt;
   28 
   29       &lt;gjob:Developers&gt;
   30         &lt;gjob:Developer&gt;
   31         &lt;/gjob:Developer&gt;
   32       &lt;/gjob:Developers&gt;
   33 
   34       &lt;gjob:Contact&gt;
   35         &lt;gjob:Person&gt;Nathan Clemons&lt;/gjob:Person&gt;
   36         &lt;gjob:Email&gt;nathan@windsofstorm.net&lt;/gjob:Email&gt;
   37         &lt;gjob:Company&gt;
   38         &lt;/gjob:Company&gt;
   39         &lt;gjob:Organisation&gt;
   40         &lt;/gjob:Organisation&gt;
   41         &lt;gjob:Webpage&gt;
   42         &lt;/gjob:Webpage&gt;
   43         &lt;gjob:Snailmail&gt;
   44         &lt;/gjob:Snailmail&gt;
   45         &lt;gjob:Phone&gt;
   46         &lt;/gjob:Phone&gt;
   47       &lt;/gjob:Contact&gt;
   48 
   49       &lt;gjob:Requirements&gt;
   50       The program should be released as free software, under the GPL.
   51       &lt;/gjob:Requirements&gt;
   52 
   53       &lt;gjob:Skills&gt;
   54       &lt;/gjob:Skills&gt;
   55 
   56       &lt;gjob:Details&gt;
   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       &lt;/gjob:Details&gt;
   65 
   66     &lt;/gjob:Job&gt;
   67 
   68   &lt;/gjob:Jobs&gt;
   69 &lt;/gjob:Helping&gt;</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>/*
   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 
   94 DEBUG("parsePerson\n");
   95     /*
   96      * allocate the struct
   97      */
   98     ret = (personPtr) malloc(sizeof(person));
   99     if (ret == NULL) {
  100         fprintf(stderr,"out of memory\n");
  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-&gt;xmlChildrenNode;
  107     while (cur != NULL) {
  108         if ((!strcmp(cur-&gt;name, "Person")) &amp;&amp; (cur-&gt;ns == ns))
  109             ret-&gt;name = xmlNodeListGetString(doc, cur-&gt;xmlChildrenNode, 1);
  110         if ((!strcmp(cur-&gt;name, "Email")) &amp;&amp; (cur-&gt;ns == ns))
  111             ret-&gt;email = xmlNodeListGetString(doc, cur-&gt;xmlChildrenNode, 1);
  112         cur = cur-&gt;next;
  113     }
  114 
  115     return(ret);
  116 }</pre><p>Here are a couple of things to notice:</p><ul>
  117   <li>Usually a recursive parsing style is the more convenient one: XML data
  118     is by nature subject to repetitive constructs and usually exhibits highly
  119     structured patterns.</li>
  120   <li>The two arguments of type <em>xmlDocPtr</em> and <em>xmlNsPtr</em>,
  121     i.e. the pointer to the global XML document and the namespace reserved to
  122     the application. Document wide information are needed for example to
  123     decode entities and it's a good coding practice to define a namespace for
  124     your application set of data and test that the element and attributes
  125     you're analyzing actually pertains to your application space. This is
  126     done by a simple equality test (cur-&gt;ns == ns).</li>
  127   <li>To retrieve text and attributes value, you can use the function
  128     <em>xmlNodeListGetString</em> to gather all the text and entity reference
  129     nodes generated by the DOM output and produce an single text string.</li>
  130 </ul><p>Here is another piece of code used to parse another level of the
  131 structure:</p><pre>#include &lt;libxml/tree.h&gt;
  132 /*
  133  * a Description for a Job
  134  */
  135 typedef struct job {
  136     char *projectID;
  137     char *application;
  138     char *category;
  139     personPtr contact;
  140     int nbDevelopers;
  141     personPtr developers[100]; /* using dynamic alloc is left as an exercise */
  142 } job, *jobPtr;
  143 
  144 /*
  145  * And the code needed to parse it
  146  */
  147 jobPtr parseJob(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
  148     jobPtr ret = NULL;
  149 
  150 DEBUG("parseJob\n");
  151     /*
  152      * allocate the struct
  153      */
  154     ret = (jobPtr) malloc(sizeof(job));
  155     if (ret == NULL) {
  156         fprintf(stderr,"out of memory\n");
  157         return(NULL);
  158     }
  159     memset(ret, 0, sizeof(job));
  160 
  161     /* We don't care what the top level element name is */
  162     cur = cur-&gt;xmlChildrenNode;
  163     while (cur != NULL) {
  164         
  165         if ((!strcmp(cur-&gt;name, "Project")) &amp;&amp; (cur-&gt;ns == ns)) {
  166             ret-&gt;projectID = xmlGetProp(cur, "ID");
  167             if (ret-&gt;projectID == NULL) {
  168                 fprintf(stderr, "Project has no ID\n");
  169             }
  170         }
  171         if ((!strcmp(cur-&gt;name, "Application")) &amp;&amp; (cur-&gt;ns == ns))
  172             ret-&gt;application = xmlNodeListGetString(doc, cur-&gt;xmlChildrenNode, 1);
  173         if ((!strcmp(cur-&gt;name, "Category")) &amp;&amp; (cur-&gt;ns == ns))
  174             ret-&gt;category = xmlNodeListGetString(doc, cur-&gt;xmlChildrenNode, 1);
  175         if ((!strcmp(cur-&gt;name, "Contact")) &amp;&amp; (cur-&gt;ns == ns))
  176             ret-&gt;contact = parsePerson(doc, ns, cur);
  177         cur = cur-&gt;next;
  178     }
  179 
  180     return(ret);
  181 }</pre><p>Once you are used to it, writing this kind of code is quite simple, but
  182 boring. Ultimately, it could be possible to write stubbers taking either C
  183 data structure definitions, a set of XML examples or an XML DTD and produce
  184 the code needed to import and export the content between C data and XML
  185 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
  186 parsing example</a> as a template, it is also available with Makefile in the
  187 Gnome SVN base under libxml2/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>