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| </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 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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>This section is directly intended to help programmers getting bootstrapped |
| using the XML tollkit from the C language. It is not intended to be |
| extensive. I hope the automatically generated documents will provide the |
| completeness required, but as a separate set of documents. The interfaces of |
| the XML parser are by principle low level, Those interested in a higher level |
| API should <a href="#DOM">look at DOM</a>.</p><p>The <a href="html/libxml-parser.html">parser interfaces for XML</a> are |
| separated from the <a href="html/libxml-htmlparser.html">HTML parser |
| 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 |
| documents either from in-memory strings or from files. The functions are |
| defined in "parser.h":</p><dl> |
| <dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt> |
| <dd><p>Parse a null-terminated string containing the document.</p> |
| </dd> |
| </dl><dl> |
| <dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt> |
| <dd><p>Parse an XML document contained in a (possibly compressed) |
| file.</p> |
| </dd> |
| </dl><p>The parser returns a pointer to the document structure (or NULL in case of |
| 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 |
| being fetched (which is common for GUI based programs) libxml2 provides a |
| push interface, too, as of version 1.8.3. Here are the interface |
| functions:</p><pre>xmlParserCtxtPtr xmlCreatePushParserCtxt(xmlSAXHandlerPtr sax, |
| void *user_data, |
| const char *chunk, |
| int size, |
| const char *filename); |
| int xmlParseChunk (xmlParserCtxtPtr ctxt, |
| const char *chunk, |
| int size, |
| int terminate);</pre><p>and here is a simple example showing how to use the interface:</p><pre> FILE *f; |
| |
| f = fopen(filename, "r"); |
| if (f != NULL) { |
| int res, size = 1024; |
| char chars[1024]; |
| xmlParserCtxtPtr ctxt; |
| |
| res = fread(chars, 1, 4, f); |
| if (res > 0) { |
| ctxt = xmlCreatePushParserCtxt(NULL, NULL, |
| chars, res, filename); |
| while ((res = fread(chars, 1, size, f)) > 0) { |
| xmlParseChunk(ctxt, chars, res, 0); |
| } |
| xmlParseChunk(ctxt, chars, 0, 1); |
| doc = ctxt->myDoc; |
| xmlFreeParserCtxt(ctxt); |
| } |
| }</pre><p>The HTML parser embedded into libxml2 also has a push interface; the |
| 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 |
| the document in memory and then building the tree itself. Reading a document |
| without building the tree is possible using the SAX interfaces (see SAX.h and |
| <a href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">James |
| Henstridge's documentation</a>). Note also that the push interface can be |
| limited to SAX: just use the two first arguments of |
| <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 |
| there is a set of functions dedicated to building new elements. (These are |
| also described in <libxml/tree.h>.) For example, here is a piece of |
| code that produces the XML document used in the previous examples:</p><pre> #include <libxml/tree.h> |
| xmlDocPtr doc; |
| xmlNodePtr tree, subtree; |
| |
| doc = xmlNewDoc("1.0"); |
| doc->children = xmlNewDocNode(doc, NULL, "EXAMPLE", NULL); |
| xmlSetProp(doc->children, "prop1", "gnome is great"); |
| xmlSetProp(doc->children, "prop2", "& linux too"); |
| tree = xmlNewChild(doc->children, NULL, "head", NULL); |
| subtree = xmlNewChild(tree, NULL, "title", "Welcome to Gnome"); |
| tree = xmlNewChild(doc->children, NULL, "chapter", NULL); |
| subtree = xmlNewChild(tree, NULL, "title", "The Linux adventure"); |
| subtree = xmlNewChild(tree, NULL, "p", "bla bla bla ..."); |
| subtree = xmlNewChild(tree, NULL, "image", NULL); |
| 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 |
| code has access to the internal structure of all the elements of the tree. |
| The names should be somewhat simple like <strong>parent</strong>, |
| <strong>children</strong>, <strong>next</strong>, <strong>prev</strong>, |
| <strong>properties</strong>, etc... For example, still with the previous |
| example:</p><pre><code>doc->children->children->children</code></pre><p>points to the title element,</p><pre>doc->children->children->next->children->children</pre><p>points to the text node containing the chapter title "The Linux |
| adventure".</p><p><strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em> to be |
| present before the document root, so <code>doc->children</code> may point |
| to an element which is not the document Root Element; a function |
| <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 |
| 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 |
| xmlChar *value);</code></dt> |
| <dd><p>This sets (or changes) an attribute carried by an ELEMENT node. |
| The value can be NULL.</p> |
| </dd> |
| </dl><dl> |
| <dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar |
| *name);</code></dt> |
| <dd><p>This function returns a pointer to new copy of the property |
| content. Note that the user must deallocate the result.</p> |
| </dd> |
| </dl><p>Two functions are provided for reading and writing the text associated |
| with elements:</p><dl> |
| <dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar |
| *value);</code></dt> |
| <dd><p>This function takes an "external" string and converts it to one |
| text node or possibly to a list of entity and text nodes. All |
| non-predefined entity references like &Gnome; will be stored |
| internally as entity nodes, hence the result of the function may not be |
| a single node.</p> |
| </dd> |
| </dl><dl> |
| <dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int |
| inLine);</code></dt> |
| <dd><p>This function is the inverse of |
| <code>xmlStringGetNodeList()</code>. It generates a new string |
| containing the content of the text and entity nodes. Note the extra |
| argument inLine. If this argument is set to 1, the function will expand |
| entity references. For example, instead of returning the &Gnome; |
| XML encoding in the string, it will substitute it with its value (say, |
| "GNU Network Object Model Environment").</p> |
| </dd> |
| </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 |
| *size);</code></dt> |
| <dd><p>Returns a buffer into which the document has been saved.</p> |
| </dd> |
| </dl><dl> |
| <dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt> |
| <dd><p>Dumps a document to an open file descriptor.</p> |
| </dd> |
| </dl><dl> |
| <dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt> |
| <dd><p>Saves the document to a file. In this case, the compression |
| interface is triggered if it has been turned on.</p> |
| </dd> |
| </dl><h3><a name="Compressio" id="Compressio">Compression</a></h3><p>The library transparently handles compression when doing file-based |
| accesses. The level of compression on saves can be turned on either globally |
| or individually for one file:</p><dl> |
| <dt><code>int xmlGetDocCompressMode (xmlDocPtr doc);</code></dt> |
| <dd><p>Gets the document compression ratio (0-9).</p> |
| </dd> |
| </dl><dl> |
| <dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt> |
| <dd><p>Sets the document compression ratio.</p> |
| </dd> |
| </dl><dl> |
| <dt><code>int xmlGetCompressMode(void);</code></dt> |
| <dd><p>Gets the default compression ratio.</p> |
| </dd> |
| </dl><dl> |
| <dt><code>void xmlSetCompressMode(int mode);</code></dt> |
| <dd><p>Sets the default compression ratio.</p> |
| </dd> |
| </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> |