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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://codespeak.net/lxml/">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><?xml version="1.0"?>
15: <gjob:Helping xmlns:gjob="http://www.gnome.org/some-location">
16: <gjob:Jobs>
17:
18: <gjob:Job>
19: <gjob:Project ID="3"/>
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>
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>/*
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->xmlChildrenNode;
107: while (cur != NULL) {
108: if ((!strcmp(cur->name, "Person")) && (cur->ns == ns))
109: ret->name = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1);
110: if ((!strcmp(cur->name, "Email")) && (cur->ns == ns))
111: ret->email = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1);
112: cur = cur->next;
113: }
114:
115: return(ret);
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>
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:
149: DEBUG("parseJob\n");
150: /*
151: * allocate the struct
152: */
153: ret = (jobPtr) malloc(sizeof(job));
154: if (ret == NULL) {
155: fprintf(stderr,"out of memory\n");
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:
164: if ((!strcmp(cur->name, "Project")) && (cur->ns == ns)) {
165: ret->projectID = xmlGetProp(cur, "ID");
166: if (ret->projectID == NULL) {
167: fprintf(stderr, "Project has no ID\n");
168: }
169: }
170: if ((!strcmp(cur->name, "Application")) && (cur->ns == ns))
171: ret->application = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1);
172: if ((!strcmp(cur->name, "Category")) && (cur->ns == ns))
173: ret->category = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1);
174: if ((!strcmp(cur->name, "Contact")) && (cur->ns == ns))
175: ret->contact = parsePerson(doc, ns, cur);
176: cur = cur->next;
177: }
178:
179: return(ret);
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 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>
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