| 1 | <?xml version="1.0" encoding="UTF-8"?>
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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 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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
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| 11 | data is not kept in the DOM tree but uses internal structures. It is based on
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| 12 | a proposal to keep a database of jobs related to Gnome, with an XML based
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| 13 | storage structure. Here is an <a href="gjobs.xml">XML encoded jobs
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| 14 | base</a>:</p><pre><?xml version="1.0"?>
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| 15 | <gjob:Helping xmlns:gjob="http://www.gnome.org/some-location">
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| 16 | <gjob:Jobs>
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| 17 |
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| 18 | <gjob:Job>
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| 19 | <gjob:Project ID="3"/>
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| 20 | <gjob:Application>GBackup</gjob:Application>
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| 21 | <gjob:Category>Development</gjob:Category>
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| 22 |
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| 23 | <gjob:Update>
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| 24 | <gjob:Status>Open</gjob:Status>
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| 25 | <gjob:Modified>Mon, 07 Jun 1999 20:27:45 -0400 MET DST</gjob:Modified>
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| 26 | <gjob:Salary>USD 0.00</gjob:Salary>
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| 27 | </gjob:Update>
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| 28 |
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| 29 | <gjob:Developers>
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| 30 | <gjob:Developer>
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| 31 | </gjob:Developer>
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| 32 | </gjob:Developers>
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| 33 |
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| 34 | <gjob:Contact>
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| 35 | <gjob:Person>Nathan Clemons</gjob:Person>
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| 36 | <gjob:Email>[email protected]</gjob:Email>
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| 37 | <gjob:Company>
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| 38 | </gjob:Company>
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| 39 | <gjob:Organisation>
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| 40 | </gjob:Organisation>
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| 41 | <gjob:Webpage>
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| 42 | </gjob:Webpage>
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| 43 | <gjob:Snailmail>
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| 44 | </gjob:Snailmail>
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| 45 | <gjob:Phone>
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| 46 | </gjob:Phone>
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| 47 | </gjob:Contact>
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| 48 |
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| 49 | <gjob:Requirements>
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| 50 | The program should be released as free software, under the GPL.
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| 51 | </gjob:Requirements>
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| 52 |
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| 53 | <gjob:Skills>
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| 54 | </gjob:Skills>
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| 55 |
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| 56 | <gjob:Details>
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| 57 | A GNOME based system that will allow a superuser to configure
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| 58 | compressed and uncompressed files and/or file systems to be backed
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| 59 | up with a supported media in the system. This should be able to
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| 60 | perform via find commands generating a list of files that are passed
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| 61 | to tar, dd, cpio, cp, gzip, etc., to be directed to the tape machine
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| 62 | or via operations performed on the filesystem itself. Email
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| 63 | notification and GUI status display very important.
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| 64 | </gjob:Details>
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| 65 |
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| 66 | </gjob:Job>
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| 67 |
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| 68 | </gjob:Jobs>
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| 69 | </gjob:Helping></pre><p>While loading the XML file into an internal DOM tree is a matter of
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| 70 | calling only a couple of functions, browsing the tree to gather the data and
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| 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
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| 72 | structure. For example, the ordering of the attributes is not significant,
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| 73 | the XML specification is clear about it. It's also usually a good idea not to
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| 74 | depend on the order of the children of a given node, unless it really makes
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| 75 | things harder. Here is some code to parse the information for a person:</p><pre>/*
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| 76 | * A person record
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| 77 | */
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| 78 | typedef struct person {
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| 79 | char *name;
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| 80 | char *email;
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| 81 | char *company;
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| 82 | char *organisation;
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| 83 | char *smail;
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| 84 | char *webPage;
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| 85 | char *phone;
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| 86 | } person, *personPtr;
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| 87 |
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| 88 | /*
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| 89 | * And the code needed to parse it
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| 90 | */
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| 91 | personPtr parsePerson(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
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| 92 | personPtr ret = NULL;
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| 93 |
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| 94 | DEBUG("parsePerson\n");
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| 95 | /*
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| 96 | * allocate the struct
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| 97 | */
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| 98 | ret = (personPtr) malloc(sizeof(person));
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| 99 | if (ret == NULL) {
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| 100 | fprintf(stderr,"out of memory\n");
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| 101 | return(NULL);
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| 102 | }
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| 103 | memset(ret, 0, sizeof(person));
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| 104 |
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| 105 | /* We don't care what the top level element name is */
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| 106 | cur = cur->xmlChildrenNode;
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| 107 | while (cur != NULL) {
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| 108 | if ((!strcmp(cur->name, "Person")) && (cur->ns == ns))
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| 109 | ret->name = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1);
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| 110 | if ((!strcmp(cur->name, "Email")) && (cur->ns == ns))
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| 111 | ret->email = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1);
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| 112 | cur = cur->next;
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| 113 | }
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| 114 |
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| 115 | return(ret);
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| 116 | }</pre><p>Here are a couple of things to notice:</p><ul>
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| 117 | <li>Usually a recursive parsing style is the more convenient one: XML data
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| 118 | is by nature subject to repetitive constructs and usually exhibits highly
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| 119 | structured patterns.</li>
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| 120 | <li>The two arguments of type <em>xmlDocPtr</em> and <em>xmlNsPtr</em>,
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| 121 | i.e. the pointer to the global XML document and the namespace reserved to
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| 122 | the application. Document wide information are needed for example to
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| 123 | decode entities and it's a good coding practice to define a namespace for
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| 124 | your application set of data and test that the element and attributes
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| 125 | you're analyzing actually pertains to your application space. This is
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| 126 | done by a simple equality test (cur->ns == ns).</li>
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| 127 | <li>To retrieve text and attributes value, you can use the function
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| 128 | <em>xmlNodeListGetString</em> to gather all the text and entity reference
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| 129 | nodes generated by the DOM output and produce an single text string.</li>
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| 130 | </ul><p>Here is another piece of code used to parse another level of the
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| 131 | structure:</p><pre>#include <libxml/tree.h>
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| 132 | /*
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| 133 | * a Description for a Job
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| 134 | */
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| 135 | typedef struct job {
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| 136 | char *projectID;
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| 137 | char *application;
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| 138 | char *category;
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| 139 | personPtr contact;
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| 140 | int nbDevelopers;
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| 141 | personPtr developers[100]; /* using dynamic alloc is left as an exercise */
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| 142 | } job, *jobPtr;
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| 143 |
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| 144 | /*
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| 145 | * And the code needed to parse it
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| 146 | */
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| 147 | jobPtr parseJob(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
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| 148 | jobPtr ret = NULL;
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| 149 |
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| 150 | DEBUG("parseJob\n");
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| 151 | /*
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| 152 | * allocate the struct
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| 153 | */
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| 154 | ret = (jobPtr) malloc(sizeof(job));
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| 155 | if (ret == NULL) {
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| 156 | fprintf(stderr,"out of memory\n");
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| 157 | return(NULL);
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| 158 | }
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| 159 | memset(ret, 0, sizeof(job));
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| 160 |
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| 161 | /* We don't care what the top level element name is */
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| 162 | cur = cur->xmlChildrenNode;
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| 163 | while (cur != NULL) {
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| 164 |
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| 165 | if ((!strcmp(cur->name, "Project")) && (cur->ns == ns)) {
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| 166 | ret->projectID = xmlGetProp(cur, "ID");
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| 167 | if (ret->projectID == NULL) {
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| 168 | fprintf(stderr, "Project has no ID\n");
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| 169 | }
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| 170 | }
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| 171 | if ((!strcmp(cur->name, "Application")) && (cur->ns == ns))
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| 172 | ret->application = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1);
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| 173 | if ((!strcmp(cur->name, "Category")) && (cur->ns == ns))
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| 174 | ret->category = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1);
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| 175 | if ((!strcmp(cur->name, "Contact")) && (cur->ns == ns))
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| 176 | ret->contact = parsePerson(doc, ns, cur);
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| 177 | cur = cur->next;
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| 178 | }
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| 179 |
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| 180 | return(ret);
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| 181 | }</pre><p>Once you are used to it, writing this kind of code is quite simple, but
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| 182 | boring. Ultimately, it could be possible to write stubbers taking either C
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| 183 | data structure definitions, a set of XML examples or an XML DTD and produce
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| 184 | the code needed to import and export the content between C data and XML
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| 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
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| 186 | parsing example</a> as a template, it is also available with Makefile in the
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| 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>
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