<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN” “www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”> <html xmlns=“www.w3.org/1999/xhtml”> http-equiv=“Content-Type” content=“text/html; charset=UTF-8” /><link rel=“SHORTCUT ICON” href=“/favicon.ico” /><style type=“text/css”> TD {font-family: Verdana,Arial,Helvetica} BODY {font-family: Verdana,Arial,Helvetica; margin-top: 2em; margin-left: 0em; margin-right: 0em} H1 {font-family: Verdana,Arial,Helvetica} H2 {font-family: Verdana,Arial,Helvetica} H3 {font-family: Verdana,Arial,Helvetica} A:link, A:visited, A:active { text-decoration: underline } </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=“swpat.ffii.org/”> src=“epatents.png” alt=“Action against software patents” /></a></td><td width=“180”><a href=“www.gnome.org/”> src=“gnome2.png” alt=“Gnome2 Logo” /></a><a href=“www.w3.org/Status”> src=“w3c.png” alt=“W3C Logo” /></a><a href=“www.redhat.com/”> src=“redhat.gif” alt=“Red Hat Logo” /></a><div align=“left”><a href=“xmlsoft.org/”> 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>Developer Menu</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>API Indexes</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>Related links</center></td></tr><tr><td bgcolor=“#fffacd”><ul><li><a href=“Mail”>mail.gnome.org/archives/xml/“>Mail archive</a></li><li><a href=”XSLT“>xmlsoft.org/XSLT/”>XSLT libxslt</a></li><li><a href=“DOM”>phd.cs.unibo.it/gdome2/“>DOM gdome2</a></li><li><a href=”XML-DSig“>www.aleksey.com/xmlsec/”>XML-DSig xmlsec</a></li><li><a href=“FTP

  • xmlsoft.org/”>FTP
  • href=“Windows”>www.zlatkovic.com/projects/libxml/“>Windows binaries</a></li><li><a href=”Solaris“>opencsw.org/packages/libxml2”>Solaris binaries</a></li><li><a href=“MacOsX”>www.explain.com.au/oss/libxml2xslt.html“>MacOsX binaries</a></li><li><a href=”lxml“>lxml.de/”>lxml Python bindings</a></li><li><a href=“Perl”>cpan.uwinnipeg.ca/dist/XML-LibXML“>Perl bindings</a></li><li><a href=”C“>libxmlplusplus.sourceforge.net/”>C++ bindings</a></li><li><a href=“PHP”>www.zend.com/php5/articles/php5-xmlphp.php#Heading4“>PHP bindings</a></li><li><a href=”Pascal“>sourceforge.net/projects/libxml2-pas/”>Pascal bindings</a></li><li><a href=“Ruby”>libxml.rubyforge.org/“>Ruby bindings</a></li><li><a href=”Tcl“>tclxml.sourceforge.net/”>Tcl bindings</a></li><li><a href=“Bug”>gitlab.gnome.org/GNOME/libxml2/issues“>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 data is not kept in the DOM tree but uses internal structures. It is based on a proposal to keep a database of jobs related to Gnome, with an XML based storage structure. Here is an <a href=”gjobs.xml“>XML encoded jobs base</a>:</p><pre>&lt;?xml version=”1.0“?&gt; &lt;gjob:Helping xmlns:gjob=”www.gnome.org/some-location“>;

    &lt;gjob:Jobs&gt;
    
      &lt;gjob:Job&gt;
        &lt;gjob:Project ID="3"/&gt;
        &lt;gjob:Application&gt;GBackup&lt;/gjob:Application&gt;
        &lt;gjob:Category&gt;Development&lt;/gjob:Category&gt;
    
        &lt;gjob:Update&gt;
          &lt;gjob:Status&gt;Open&lt;/gjob:Status&gt;
          &lt;gjob:Modified&gt;Mon, 07 Jun 1999 20:27:45 -0400 MET DST&lt;/gjob:Modified&gt;
          &lt;gjob:Salary&gt;USD 0.00&lt;/gjob:Salary&gt;
        &lt;/gjob:Update&gt;
    
        &lt;gjob:Developers&gt;
          &lt;gjob:Developer&gt;
          &lt;/gjob:Developer&gt;
        &lt;/gjob:Developers&gt;
    
        &lt;gjob:Contact&gt;
          &lt;gjob:Person&gt;Nathan Clemons&lt;/gjob:Person&gt;
          &lt;gjob:Email&gt;nathan@windsofstorm.net&lt;/gjob:Email&gt;
          &lt;gjob:Company&gt;
          &lt;/gjob:Company&gt;
          &lt;gjob:Organisation&gt;
          &lt;/gjob:Organisation&gt;
          &lt;gjob:Webpage&gt;
          &lt;/gjob:Webpage&gt;
          &lt;gjob:Snailmail&gt;
          &lt;/gjob:Snailmail&gt;
          &lt;gjob:Phone&gt;
          &lt;/gjob:Phone&gt;
        &lt;/gjob:Contact&gt;
    
        &lt;gjob:Requirements&gt;
        The program should be released as free software, under the GPL.
        &lt;/gjob:Requirements&gt;
    
        &lt;gjob:Skills&gt;
        &lt;/gjob:Skills&gt;
    
        &lt;gjob:Details&gt;
        A GNOME based system that will allow a superuser to configure 
        compressed and uncompressed files and/or file systems to be backed 
        up with a supported media in the system.  This should be able to 
        perform via find commands generating a list of files that are passed 
        to tar, dd, cpio, cp, gzip, etc., to be directed to the tape machine 
        or via operations performed on the filesystem itself. Email 
        notification and GUI status display very important.
        &lt;/gjob:Details&gt;
    
      &lt;/gjob:Job&gt;
    
    &lt;/gjob:Jobs&gt;

    &lt;/gjob:Helping&gt;</pre><p>While loading the XML file into an internal DOM tree is a matter of calling only a couple of functions, browsing the tree to gather the data and generate the internal structures is harder, and more error prone.</p><p>The suggested principle is to be tolerant with respect to the input structure. For example, the ordering of the attributes is not significant, the XML specification is clear about it. It's also usually a good idea not to depend on the order of the children of a given node, unless it really makes things harder. Here is some code to parse the information for a person:</p><pre>

    A person record
    

    typedef struct person {

    char *name;
    char *email;
    char *company;
    char *organisation;
    char *smail;
    char *webPage;
    char *phone;
    

    } person, *personPtr;

     And the code needed to parse it
    /

    personPtr parsePerson(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {

    personPtr ret = NULL;
    

    DEBUG(“parsePersonn”);

    /*
       allocate the struct
      /
    ret = (personPtr) malloc(sizeof(person));
    if (ret == NULL) {
        fprintf(stderr,"out of memory\n");
        return(NULL);
    }
    memset(ret, 0, sizeof(person));
    
    /* We don't care what the top level element name is   
    cur = cur-&gt;xmlChildrenNode;
    while (cur != NULL) {
        if ((!strcmp(cur-&gt;name, "Person")) &amp;&amp; (cur-&gt;ns == ns))
            ret-&gt;name = xmlNodeListGetString(doc, cur-&gt;xmlChildrenNode, 1);
        if ((!strcmp(cur-&gt;name, "Email")) &amp;&amp; (cur-&gt;ns == ns))
            ret-&gt;email = xmlNodeListGetString(doc, cur-&gt;xmlChildrenNode, 1);
        cur = cur-&gt;next;
    }
    
    return(ret);

    }</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
      is by nature subject to repetitive constructs and usually exhibits highly
      structured patterns.</li>
    <li>The two arguments of type <em>xmlDocPtr</em> and <em>xmlNsPtr</em>,
      i.e. the pointer to the global XML document and the namespace reserved to
      the application. Document wide information are needed for example to
      decode entities and it's a good coding practice to define a namespace for
      your application set of data and test that the element and attributes
      you're analyzing actually pertains to your application space. This is
      done by a simple equality test (cur-&gt;ns == ns).</li>
    <li>To retrieve text and attributes value, you can use the function
      <em>xmlNodeListGetString</em> to gather all the text and entity reference
      nodes generated by the DOM output and produce an single text string.</li>

    </ul><p>Here is another piece of code used to parse another level of the structure:</p><pre>#include &lt;libxml/tree.h&gt; /*

     a Description for a Job
    /

    typedef struct job {

    char *projectID;
    char *application;
    char *category;
    personPtr contact;
    int nbDevelopers;
    personPtr developers[100]; /* using dynamic alloc is left as an exercise */

    } job, *jobPtr;

    /*

     And the code needed to parse it
    /

    jobPtr parseJob(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {

    jobPtr ret = NULL;
    

    DEBUG(“parseJobn”);

    /*
       allocate the struct
      /
    ret = (jobPtr) malloc(sizeof(job));
    if (ret == NULL) {
        fprintf(stderr,"out of memory\n");
        return(NULL);
    }
    memset(ret, 0, sizeof(job));
    
    /* We don't care what the top level element name is */
    cur = cur-&gt;xmlChildrenNode;
    while (cur != NULL) {
    
        if ((!strcmp(cur-&gt;name, "Project")) &amp;&amp; (cur-&gt;ns == ns)) {
            ret-&gt;projectID = xmlGetProp(cur, "ID");
            if (ret-&gt;projectID == NULL) {
                fprintf(stderr, "Project has no ID\n");
            }
        }
        if ((!strcmp(cur-&gt;name, "Application")) &amp;&amp; (cur-&gt;ns == ns))
            ret-&gt;application = xmlNodeListGetString(doc, cur-&gt;xmlChildrenNode, 1);
        if ((!strcmp(cur-&gt;name, "Category")) &amp;&amp; (cur-&gt;ns == ns))
            ret-&gt;category = xmlNodeListGetString(doc, cur-&gt;xmlChildrenNode, 1);
        if ((!strcmp(cur-&gt;name, "Contact")) &amp;&amp; (cur-&gt;ns == ns))
            ret-&gt;contact = parsePerson(doc, ns, cur);
        cur = cur-&gt;next;
    }
    
    return(ret);

    }</pre><p>Once you are used to it, writing this kind of code is quite simple, but boring. Ultimately, it could be possible to write stubbers taking either C data structure definitions, a set of XML examples or an XML DTD and produce the code needed to import and export the content between C data and XML 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 parsing example</a> as a template, it is also available with Makefile in the 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>