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  10 </style><title>The parser interfaces</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>The parser interfaces</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>This section is directly intended to help programmers getting bootstrapped
  11 using the XML tollkit from the C language. It is not intended to be
  12 extensive. I hope the automatically generated documents will provide the
  13 completeness required, but as a separate set of documents. The interfaces of
  14 the XML parser are by principle low level, Those interested in a higher level
  15 API should <a href="#DOM">look at DOM</a>.</p><p>The <a href="html/libxml-parser.html">parser interfaces for XML</a> are
  16 separated from the <a href="html/libxml-htmlparser.html">HTML parser
  17 interfaces</a>.  Let's have a look at how the XML parser can be called:</p><h3><a name="Invoking" id="Invoking">Invoking the parser : the pull method</a></h3><p>Usually, the first thing to do is to read an XML input. The parser accepts
  18 documents either from in-memory strings or from files.  The functions are
  19 defined in "parser.h":</p><dl><dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt>
  20     <dd><p>Parse a null-terminated string containing the document.</p>
  21     </dd>
  22 </dl><dl><dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt>
  23     <dd><p>Parse an XML document contained in a (possibly compressed)
  24       file.</p>
  25     </dd>
  26 </dl><p>The parser returns a pointer to the document structure (or NULL in case of
  27 failure).</p><h3 id="Invoking1">Invoking the parser: the push method</h3><p>In order for the application to keep the control when the document is
  28 being fetched (which is common for GUI based programs) libxml2 provides a
  29 push interface, too, as of version 1.8.3. Here are the interface
  30 functions:</p><pre>xmlParserCtxtPtr xmlCreatePushParserCtxt(xmlSAXHandlerPtr sax,
  31                                          void *user_data,
  32                                          const char *chunk,
  33                                          int size,
  34                                          const char *filename);
  35 int              xmlParseChunk          (xmlParserCtxtPtr ctxt,
  36                                          const char *chunk,
  37                                          int size,
  38                                          int terminate);</pre><p>and here is a simple example showing how to use the interface:</p><pre>            FILE *f;
  39
  40             f = fopen(filename, "r");
  41             if (f != NULL) {
  42                 int res, size = 1024;
  43                 char chars[1024];
  44                 xmlParserCtxtPtr ctxt;
  45
  46                 res = fread(chars, 1, 4, f);
  47                 if (res &gt; 0) {
  48                     ctxt = xmlCreatePushParserCtxt(NULL, NULL,
  49                                 chars, res, filename);
  50                     while ((res = fread(chars, 1, size, f)) &gt; 0) {
  51                         xmlParseChunk(ctxt, chars, res, 0);
  52                     }
  53                     xmlParseChunk(ctxt, chars, 0, 1);
  54                     doc = ctxt-&gt;myDoc;
  55                     xmlFreeParserCtxt(ctxt);
  56                 }
  57             }</pre><p>The HTML parser embedded into libxml2 also has a push interface; the
  58 functions are just prefixed by "html" rather than "xml".</p><h3 id="Invoking2">Invoking the parser: the SAX interface</h3><p>The tree-building interface makes the parser memory-hungry, first loading
  59 the document in memory and then building the tree itself. Reading a document
  60 without building the tree is possible using the SAX interfaces (see SAX.h and
  61 <a href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">James
  62 Henstridge's documentation</a>). Note also that the push interface can be
  63 limited to SAX: just use the two first arguments of
  64 <code>xmlCreatePushParserCtxt()</code>.</p><h3><a name="Building" id="Building">Building a tree from scratch</a></h3><p>The other way to get an XML tree in memory is by building it. Basically
  65 there is a set of functions dedicated to building new elements. (These are
  66 also described in &lt;libxml/tree.h&gt;.) For example, here is a piece of
  67 code that produces the XML document used in the previous examples:</p><pre>    #include &lt;libxml/tree.h&gt;
  68     xmlDocPtr doc;
  69     xmlNodePtr tree, subtree;
  70
  71     doc = xmlNewDoc("1.0");
  72     doc-&gt;children = xmlNewDocNode(doc, NULL, "EXAMPLE", NULL);
  73     xmlSetProp(doc-&gt;children, "prop1", "gnome is great");
  74     xmlSetProp(doc-&gt;children, "prop2", "&amp; linux too");
  75     tree = xmlNewChild(doc-&gt;children, NULL, "head", NULL);
  76     subtree = xmlNewChild(tree, NULL, "title", "Welcome to Gnome");
  77     tree = xmlNewChild(doc-&gt;children, NULL, "chapter", NULL);
  78     subtree = xmlNewChild(tree, NULL, "title", "The Linux adventure");
  79     subtree = xmlNewChild(tree, NULL, "p", "bla bla bla ...");
  80     subtree = xmlNewChild(tree, NULL, "image", NULL);
  81     xmlSetProp(subtree, "href", "linus.gif");</pre><p>Not really rocket science ...</p><h3><a name="Traversing" id="Traversing">Traversing the tree</a></h3><p>Basically by <a href="html/libxml-tree.html">including "tree.h"</a> your
  82 code has access to the internal structure of all the elements of the tree.
  83 The names should be somewhat simple like <strong>parent</strong>,
  84 <strong>children</strong>, <strong>next</strong>, <strong>prev</strong>,
  85 <strong>properties</strong>, etc... For example, still with the previous
  86 example:</p><pre><code>doc-&gt;children-&gt;children-&gt;children</code></pre><p>points to the title element,</p><pre>doc-&gt;children-&gt;children-&gt;next-&gt;children-&gt;children</pre><p>points to the text node containing the chapter title "The Linux
  87 adventure".</p><p><strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em> to be
  88 present before the document root, so <code>doc-&gt;children</code> may point
  89 to an element which is not the document Root Element; a function
  90 <code>xmlDocGetRootElement()</code> was added for this purpose.</p><h3><a name="Modifying" id="Modifying">Modifying the tree</a></h3><p>Functions are provided for reading and writing the document content. Here
  91 is an excerpt from the <a href="html/libxml-tree.html">tree API</a>:</p><dl><dt><code>xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, const
  92   xmlChar *value);</code></dt>
  93     <dd><p>This sets (or changes) an attribute carried by an ELEMENT node.
  94       The value can be NULL.</p>
  95     </dd>
  96 </dl><dl><dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar
  97   *name);</code></dt>
  98     <dd><p>This function returns a pointer to new copy of the property
  99       content. Note that the user must deallocate the result.</p>
 100     </dd>
 101 </dl><p>Two functions are provided for reading and writing the text associated
 102 with elements:</p><dl><dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar
 103   *value);</code></dt>
 104     <dd><p>This function takes an "external" string and converts it to one
 105       text node or possibly to a list of entity and text nodes. All
 106       non-predefined entity references like &amp;Gnome; will be stored
 107       internally as entity nodes, hence the result of the function may not be
 108       a single node.</p>
 109     </dd>
 110 </dl><dl><dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int
 111   inLine);</code></dt>
 112     <dd><p>This function is the inverse of
 113       <code>xmlStringGetNodeList()</code>. It generates a new string
 114       containing the content of the text and entity nodes. Note the extra
 115       argument inLine. If this argument is set to 1, the function will expand
 116       entity references.  For example, instead of returning the &amp;Gnome;
 117       XML encoding in the string, it will substitute it with its value (say,
 118       "GNU Network Object Model Environment").</p>
 119     </dd>
 120 </dl><h3><a name="Saving" id="Saving">Saving a tree</a></h3><p>Basically 3 options are possible:</p><dl><dt><code>void xmlDocDumpMemory(xmlDocPtr cur, xmlChar**mem, int
 121   *size);</code></dt>
 122     <dd><p>Returns a buffer into which the document has been saved.</p>
 123     </dd>
 124 </dl><dl><dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt>
 125     <dd><p>Dumps a document to an open file descriptor.</p>
 126     </dd>
 127 </dl><dl><dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt>
 128     <dd><p>Saves the document to a file. In this case, the compression
 129       interface is triggered if it has been turned on.</p>
 130     </dd>
 131 </dl><h3><a name="Compressio" id="Compressio">Compression</a></h3><p>The library transparently handles compression when doing file-based
 132 accesses. The level of compression on saves can be turned on either globally
 133 or individually for one file:</p><dl><dt><code>int  xmlGetDocCompressMode (xmlDocPtr doc);</code></dt>
 134     <dd><p>Gets the document compression ratio (0-9).</p>
 135     </dd>
 136 </dl><dl><dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt>
 137     <dd><p>Sets the document compression ratio.</p>
 138     </dd>
 139 </dl><dl><dt><code>int  xmlGetCompressMode(void);</code></dt>
 140     <dd><p>Gets the default compression ratio.</p>
 141     </dd>
 142 </dl><dl><dt><code>void xmlSetCompressMode(int mode);</code></dt>
 143     <dd><p>Sets the default compression ratio.</p>
 144     </dd>
 145 </dl><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>